[media] staging: lirc: Fix sparse warnings

Fix sparse warnings by adding __user and __iomem annotations where
necessary and removing certain unnecessary casts. While at it,
also use u32 in place of __u32.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>