lib/parser.c: switch match_u64int() over to use match_strdup()

This simplifies the code.  No change in behavior.

Link: http://lkml.kernel.org/r/20180830194814.192880-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.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>

lib/parser.c

@@ -166,13 +166,10 @@ static int match_u64int(substring_t *s, u64 *result, int base)
 	char *buf;
 	int ret;
 	u64 val;
-	size_t len = s->to - s->from;
 
-	buf = kmalloc(len + 1, GFP_KERNEL);
+	buf = match_strdup(s);
 	if (!buf)
 		return -ENOMEM;
-	memcpy(buf, s->from, len);
-	buf[len] = '\0';
 
 	ret = kstrtoull(buf, base, &val);
 	if (!ret)