XFS: Use a signed return type for suffix_kstrtoint()
The return type "unsigned long" was used by the suffix_kstrtoint()
function even though it will eventually return a negative error code.
Improve this implementation detail by using the type "int" instead.
This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net> Reviewed-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>