checkpatch: tweak "struct should normally be const" warning

Avoid triggering on

    typedef struct BlockJobDriver BlockJobDriver;

or

    struct BlockJobDriver {

Cc: John Snow <jsnow@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

scripts/checkpatch.pl

@@ -2498,8 +2498,8 @@ sub process {
 				VMStateDescription|
 				VMStateInfo}x;
 		if ($line !~ /\bconst\b/ &&
-		    $line =~ /\b($struct_ops)\b/) {
-			ERROR("struct $1 should normally be const\n" .
+		    $line =~ /\b($struct_ops)\b.*=/) {
+			ERROR("initializer for struct $1 should normally be const\n" .
 				$herecurr);
 		}