media: smiapp: Refactor reading SMIA limits

Combine the two trivial functions reading limits into one. Also rename
smiapp_get_all_limits() as smiapp_read_all_smia_limits().

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>