Fix Configure test for -mips in CFLAGS

We want to add -mips2 or -mips3 only if the user hasn't already
specified a mips version in CFLAGS. The existing test was a
double-negative.

CLA: trivial

Fixes: #20214

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from #20536)

Configure

@@ -1244,7 +1244,7 @@ if ($target =~ /^mingw/ && `$config{CC} --target-help 2>&1` =~ m/-mno-cygwin/m)
         }
 
 if ($target =~ /linux.*-mips/ && !$disabled{asm}
-        && !grep { $_ !~ /-m(ips|arch=)/ } (@{$config{CFLAGS}})) {
+        && !grep { $_ =~ /-m(ips|arch=)/ } (@{$config{CFLAGS}})) {
         # minimally required architecture flags for assembly modules
         my $value;
         $value = '-mips2' if ($target =~ /mips32/);