use qemu_free() instead of free()

There is a call to free() where qemu_free() should instead be used.

Signed-off-by: Bruce Rogers <brogers@novell.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index c134c2b..96ef1b1 100644
--- a/block.c
+++ b/block.c
@@ -2075,7 +2075,7 @@
     return 0;
 
 fail:
-    free(mcb);
+    qemu_free(mcb);
     return -1;
 }