ppc4xx: Fixed PPC4xx debug compilation error in uic.c

This patch fixes a debug compilation error for PPC4xx platforms, all
other architectures are not affected by this change.  The 'handler'
pointer was undefined.  The fix is exercised and has effect only if
DEBUG is defined.

Signed-off-by: Alessio Centazzo <acpatin@yahoo.com>
Signed-off-by: Stefan Roese <sr@denx.de>