drm_proc.c fix compilation warning

 drivers/gpu/drm/drm_proc.c: In function ‘drm__vma_info’:
 drivers/gpu/drm/drm_proc.c:681: warning: format ‘%08lx’ expects type ‘long unsigned int’, but argument 5 has type ‘phys_addr_t’

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>