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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>