drm/i915/xehp: Fix missing sentinel on mcr_ranges_xehp

drm/i915/xehp: Fix missing sentinel on mcr_ranges_xehp

There's a missing sentinel since we are not using ARRAY_SIZE(), but rather
checking that the .start is 0 to stop the iteration in mcr_range().

	BUG: KASAN: global-out-of-bounds in mcr_range.isra.0+0x69/0xa0 [i915]
	Read of size 4 at addr ffffffffa0889928 by task modprobe/3881

Fixes: d8905ba705ab ("drm/i915/xehp: Define multicast register ranges")
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730191115.2514581-1-lucas.demarchi@intel.com