drm/vc4: fix warning in validate printf.

This just fixes a warning on 64-bit builds:

  drivers/gpu/drm/vc4/vc4_validate.c: In function ‘validate_gl_shader_rec’:
  drivers/gpu/drm/vc4/vc4_validate.c:864:12: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘size_t {aka long unsigned int}’ [-Wformat=]

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>