staging/lustre/vvp: release mmap_sem in error case

The mmap_sem is downed in vvp_mmap_locks, but in case of
error from cl_io_lock_alloc_add, it is not upped.

Credit to Paul Casella at Cray for finding this.
Signed-off-by: Patrick Farrell <paf@cray.com>
Reviewed-on: http://review.whamcloud.com/10741
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5221Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/vvp_io.c

@@ -269,8 +269,10 @@ static int vvp_mmap_locks(const struct lu_env *env,
 			       descr->cld_mode, descr->cld_start,
 			       descr->cld_end);
 
-			if (result < 0)
+			if (result < 0) {
+				up_read(&mm->mmap_sem);
 				return result;
+			}
 
 			if (vma->vm_end - addr >= count)
 				break;