c_rehash: Fix file extension matching

For some reason, parenthesis were added 8 years ago in commit
a787c2590e468585a1a19738e0c7f481ec91b762. This essentially removed the
\. and $ constructs from the middle branches. Hence a file called e.g.
cert.key would accidentally match the (cer) rule.

CLA: trivial

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19427)

tools/c_rehash.in

@@ -143,7 +143,7 @@ sub hash_dir {
             }
         }
     }
-    FILE: foreach $fname (grep {/\.(pem)|(crt)|(cer)|(crl)$/} @flist) {
+    FILE: foreach $fname (grep {/\.(pem|crt|cer|crl)$/} @flist) {
         # Check to see if certificates and/or CRLs present.
         my ($cert, $crl) = check_file($fname);
         if (!$cert && !$crl) {