drm/r128: Fix undefined behavior due to shift overflowing the constant

Fix:

  drivers/gpu/drm/r128/r128_cce.c: In function ‘r128_do_init_cce’:
  drivers/gpu/drm/r128/r128_cce.c:417:2: error: case label does not reduce to an integer constant
    case R128_PM4_64BM_64VCBM_64INDBM:
    ^~~~
  drivers/gpu/drm/r128/r128_cce.c:418:2: error: case label does not reduce to an integer constant
    case R128_PM4_64PIO_64VCPIO_64INDPIO:
    ^~~~

See https://lore.kernel.org/r/YkwQ6%2BtIH8GQpuct@zn.tnic

 for the gory
details as to why it triggers with older gccs only.

Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220405151517.29753-5-bp@alien8.de