[MIPS] TLBRET_DIRTY is a valid return value from get_physical_address

Change-Id: I3ddfd3de165575c52a76cf9acee1e304d42562cf
Signed-off-by: Chris Dearman <chris@mips.com>
diff --git a/target-mips/helper.c b/target-mips/helper.c
index ec87114..12caf34 100644
--- a/target-mips/helper.c
+++ b/target-mips/helper.c
@@ -324,7 +324,7 @@
     access_type = ACCESS_INT;
     ret = get_physical_address(env, &physical, &prot,
                                address, rw, access_type);
-    if (ret != TLBRET_MATCH) {
+    if (ret != TLBRET_MATCH || ret != TLBRET_DIRTY) {
         raise_mmu_exception(env, address, rw, ret);
         return -1LL;
     } else {