fs/userfaultfd.c: remove redundant pointer uwq

fs/userfaultfd.c: remove redundant pointer uwq

Pointer uwq is being assigned but is never used hence it is redundant
and can be removed.

Cleans up clang warning:
  warning: variable 'uwq' set but not used [-Wunused-but-set-variable]

Link: http://lkml.kernel.org/r/20180717090802.18357-1-colin.king@canonical.com
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>