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

fs/fuse/file.c

@@ -1922,7 +1922,7 @@ unsigned fuse_file_poll(struct file *file, poll_table *wait)
 
 	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;