fix r54203's typo (no DLONG case)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54206 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

internal.h

@@ -284,11 +284,11 @@ rb_fix_mul_fix(VALUE x, VALUE y)
 #ifdef DLONG
     return DL2NUM((DLONG)lx * (DLONG)ly);
 #else
-    if (MUL_OVERFLOW_FIXNUM_P(a, b)) {
-	return rb_big_mul(rb_int2big(a), rb_int2big(b));
+    if (MUL_OVERFLOW_FIXNUM_P(x, y)) {
+	return rb_big_mul(rb_int2big(x), rb_int2big(y));
     }
     else {
-	return LONG2FIX(a * b);
+	return LONG2FIX(x * y);
     }
 #endif
 }