mdio, phy: fix -Wshadow warnings triggered by nested container_of()

mdio, phy: fix -Wshadow warnings triggered by nested container_of()

container_of() macro hides a local variable '__mptr' inside. This
becomes a problem when several container_of() are nested in each
other within single line or plain macros.
As C preprocessor doesn't support generating random variable names,
the sole solution is to avoid defining macros that consist only of
container_of() calls, or they will self-shadow '__mptr' each time:

In file included from ./include/linux/bitmap.h:10,
                 from drivers/net/phy/phy_device.c:12:
drivers/net/phy/phy_device.c: In function ‘phy_device_release’:
./include/linux/kernel.h:693:8: warning: declaration of ‘__mptr’ shadows a previous local [-Wshadow]
  693 |  void *__mptr = (void *)(ptr);     \
      |        ^~~~~~
./include/linux/phy.h:647:26: note: in expansion of macro ‘container_of’
  647 | #define to_phy_device(d) container_of(to_mdio_device(d), \
      |                          ^~~~~~~~~~~~
./include/linux/mdio.h:52:27: note: in expansion of macro ‘container_of’
   52 | #define to_mdio_device(d) container_of(d, struct mdio_device, dev)
      |                           ^~~~~~~~~~~~
./include/linux/phy.h:647:39: note: in expansion of macro ‘to_mdio_device’
  647 | #define to_phy_device(d) container_of(to_mdio_device(d), \
      |                                       ^~~~~~~~~~~~~~
drivers/net/phy/phy_device.c:217:8: note: in expansion of macro ‘to_phy_device’
  217 |  kfree(to_phy_device(dev));
      |        ^~~~~~~~~~~~~
./include/linux/kernel.h:693:8: note: shadowed declaration is here
  693 |  void *__mptr = (void *)(ptr);     \
      |        ^~~~~~
./include/linux/phy.h:647:26: note: in expansion of macro ‘container_of’
  647 | #define to_phy_device(d) container_of(to_mdio_device(d), \
      |                          ^~~~~~~~~~~~
drivers/net/phy/phy_device.c:217:8: note: in expansion of macro ‘to_phy_device’
  217 |  kfree(to_phy_device(dev));
      |        ^~~~~~~~~~~~~

As they are declared in header files, these warnings are highly
repetitive and very annoying (along with the one from linux/pci.h).

Convert the related macros from linux/{mdio,phy}.h to static inlines
to avoid self-shadowing and potentially improve bug-catching.
No functional changes implied.

Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20210116161246.67075-1-alobakin@pm.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>