video: ati_radeon_fb.c: fix warning while compiling with DEBUG

Fixes this warning:

ati_radeon_fb.c: In function 'radeon_probe':
ati_radeon_fb.c:598: warning: format '%x' expects type 'unsigned int',
but argument 2 has type 'void *'

Signed-off-by: Anatolij Gustschin <agust@denx.de>