[media] smiapp: Rename SMIA_REG to SMIAPP_REG for consistency

SMIAPP_REG_ is the common prefix used in the driver for register related
definitions. Use it consistently.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>