nfsd: add get_uint for u32's

commit a007c4c3e943ecc054a806c259d95420a188754b upstream.

I don't think there's a practical difference for the range of values
these interfaces should see, but it would be safer to be unambiguous.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>