Fix a typo in the return type of dvmIsValidCard.

Change-Id: I518751b338e373d63a975c55320200348fa94b91
diff --git a/vm/alloc/CardTable.h b/vm/alloc/CardTable.h
index fca6907..a6f2b38 100644
--- a/vm/alloc/CardTable.h
+++ b/vm/alloc/CardTable.h
@@ -58,7 +58,7 @@
 /*
  * Returns true if addr points to a valid card.
  */
-void dvmIsValidCard(const u1 *card);
+bool dvmIsValidCard(const u1 *card);
 
 /*
  * Set the card associated with the given address to GC_CARD_DIRTY.