lib/string.c: simplify str[c]spn

Use strchr(), which makes them a lot shorter, and more obviously symmetric
in their treatment of accept/reject.  It also saves a little bit of .text;
bloat-o-meter for an arm build says

Function                                     old     new   delta
strcspn                                       92      76     -16
strspn                                       108      76     -32

While here, also remove a stray empty line before EXPORT_SYMBOL().

Link: https://lkml.kernel.org/r/20220328224119.3003834-2-linux@rasmusvillemoes.dkSigned-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/string.c

@@ -517,21 +517,13 @@ EXPORT_SYMBOL(strnlen);
 size_t strspn(const char *s, const char *accept)
 {
 	const char *p;
-	const char *a;
-	size_t count = 0;
 
 	for (p = s; *p != '\0'; ++p) {
-		for (a = accept; *a != '\0'; ++a) {
-			if (*p == *a)
-				break;
-		}
-		if (*a == '\0')
-			return count;
-		++count;
+		if (!strchr(accept, *p))
+			break;
 	}
-	return count;
+	return p - s;
 }
-
 EXPORT_SYMBOL(strspn);
 #endif
 
@@ -544,17 +536,12 @@ EXPORT_SYMBOL(strspn);
 size_t strcspn(const char *s, const char *reject)
 {
 	const char *p;
-	const char *r;
-	size_t count = 0;
 
 	for (p = s; *p != '\0'; ++p) {
-		for (r = reject; *r != '\0'; ++r) {
-			if (*p == *r)
-				return count;
-		}
-		++count;
+		if (strchr(reject, *p))
+			break;
 	}
-	return count;
+	return p - s;
 }
 EXPORT_SYMBOL(strcspn);
 #endif