samsung-laptop: cleanup return type: mode_t vs umode_t

This function returns a umode_t (unsigned short) instead of mode_t which
is an unsigned int on some architectures.  Cleaning this up silences a
compile warning:

drivers/platform/x86/samsung-laptop.c:1108:2: warning: initialization
	from incompatible pointer type [enabled by default]

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Matthew Garrett <mjg@redhat.com>