fuse: fix bad return value in fuse_file_poll()

Fix fuse_file_poll() which returned a -errno value instead of a poll
mask.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: stable@kernel.org
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index fce6ce6..cbc4640 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1922,7 +1922,7 @@
 
 	req = fuse_get_req(fc);
 	if (IS_ERR(req))
-		return PTR_ERR(req);
+		return POLLERR;
 
 	req->in.h.opcode = FUSE_POLL;
 	req->in.h.nodeid = ff->nodeid;