drm/i915: fix command parser debug print format mismatches

Drop the cast from the pointer diff to fix:

drivers/gpu/drm/i915/i915_cmd_parser.c:405:4: warning: format '%td' expects
argument of type 'ptrdiff_t', but argument 5 has type 'long unsigned int'
[-Wformat]

While at it, use %u for u32.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
[danvet: After conflict resolution only the "While at it, ..." part
was left standing ...]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>