tools: kwbimage: Fix printf format warning

tools: kwbimage: Fix printf format warning

On 32-bit ARM the compiler complains:
  tools/kwbimage.c:547: warning: format ‘%lu’ expects argument of type
                                 ‘long unsigned int’, but argument 4 has
		                 type ‘unsigned int’

Fix this by using %zu instead of %lu format specifier.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
[jh80.chung: cherry picked from mainline commit 3b5da64edfdc013b105573a20871659d37ab53de]

Change-Id: I058d4395fd8e6cab5ee593974173f97929ec6a55
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>