media: smiapp: Use unaligned get and put functions

Use get_unaligned_be* and put_unaligned_be* functions to convert register
values to CPU endianness. Consequently, two instances of BUG() are
removed.

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