i3c: master: svc: Describe member 'saved_regs'

i3c: master: svc: Describe member 'saved_regs'

The 'saved_regs' member of the 'svc_i3c_master'	structure is not
described in the kernel doc, which produces the following warning:

    Function parameter or member 'saved_regs' not described in 'svc_i3c_master'

Add the missing line in the kernel documentation of the parent
structure.

Fixes: 1c5ee2a77b1b ("i3c: master: svc: fix i3c suspend/resume issue")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202308171435.0xQ82lvu-lkp@intel.com/
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20230817101853.16805-1-miquel.raynal@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>