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

This simplifies the code.  No change in behavior.

Link: http://lkml.kernel.org/r/20180830194436.188867-1-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

@@ -327,10 +327,6 @@ EXPORT_SYMBOL(match_strlcpy);
  */
 char *match_strdup(const substring_t *s)
 {
-	size_t sz = s->to - s->from + 1;
-	char *p = kmalloc(sz, GFP_KERNEL);
-	if (p)
-		match_strlcpy(p, s, sz);
-	return p;
+	return kmemdup_nul(s->from, s->to - s->from, GFP_KERNEL);
 }
 EXPORT_SYMBOL(match_strdup);