console: Fix qemu_default_pixelformat() for 24 bpp

Falls through to 32 bpp.  Harmless, because the only difference is the
alpha component, and we're not using that.  Spotted by Coverity.

Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

console.c

@@ -1688,6 +1688,7 @@ PixelFormat qemu_default_pixelformat(int bpp)
             pf.rbits = 8;
             pf.gbits = 8;
             pf.bbits = 8;
+            break;
         case 32:
             pf.rmask = 0x00FF0000;
             pf.gmask = 0x0000FF00;