splice: fix error return code

fs/splice.c: In function 'default_file_splice_read':
fs/splice.c:566: warning: 'error' may be used uninitialized in this function

which is sort-of true.  The code will in fact return -ENOMEM instead of the
kernel_readv() return value.

Cc: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

fs/splice.c

@@ -595,8 +595,10 @@ ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
 	}
 
 	res = kernel_readv(in, vec, spd.nr_pages, *ppos);
-	if (res < 0)
+	if (res < 0) {
+		error = res;
 		goto err;
+	}
 
 	error = 0;
 	if (!res)