[media] stk-webcam: fix an endian bug in stk_camera_read_reg()

We pass an int pointer to stk_camera_read_reg() but only write to the
highest byte.  It's a bug on big endian systems and generally a nasty
thing to do and doesn't match the write function either.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>