eth: fs_enet: fix print format for resource size

eth: fs_enet: fix print format for resource size

Randy reported that linux-next build warns on PowerPC:

drivers/net/ethernet/freescale/fs_enet/mii-fec.c: In function 'fs_enet_mdio_probe':
drivers/net/ethernet/freescale/fs_enet/mii-fec.c:130:50: warning: format '%x' expects argument of type 'unsigned int', but argument 4 has type 'resource_size_t' {aka 'long long unsigned int'} [-Wformat=]
  130 |         snprintf(new_bus->id, MII_BUS_ID_SIZE, "%x", res.start);
      |                                                 ~^   ~~~~~~~~~
      |                                                  |      |
      |                                                  |      resource_size_t {aka long long unsigned int}
      |                                                  unsigned int
      |                                                 %llx

Use the right print format.

Link: https://lore.kernel.org/all/8f9f8d38-d9c7-9f1b-feb0-103d76902d14@infradead.org/
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Link: https://lore.kernel.org/r/20230615035231.2184880-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>