selinux: avoid implicit conversions in selinuxfs code

Use umode_t as parameter type for sel_make_inode(), which assigns the
value to the member i_mode of struct inode.

Use identical and unsigned types for loop iterators.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>