Fixed pc-bios path in standalone emulator

pc-bios was recently moved to new directory.  Change emulator to
search in new path in standalone mode (built in external/qemu
and run from external/qemu/objs).  To be specific, change

../../../prebuilt/common/pc-bios/

to

../../../prebuilts/qemu-kernel/x86/pc-bios/

Change-Id: Id79534349394c9b47f8ef5dda76f2a21268b58fe
diff --git a/vl-android.c b/vl-android.c
index b43f7fe..74a2dc4 100644
--- a/vl-android.c
+++ b/vl-android.c
@@ -2271,7 +2271,7 @@
             buf = qemu_find_file_with_subdir(data_dir, "../usr/share/pc-bios/", name);
         /* Finally, try this for standalone builds under external/qemu */
         if (buf == NULL)
-            buf = qemu_find_file_with_subdir(data_dir, "../../../prebuilt/common/pc-bios/", name);
+            buf = qemu_find_file_with_subdir(data_dir, "../../../prebuilts/qemu-kernel/x86/pc-bios/", name);
     }
 #endif
     return buf;