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: d8905ba ("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

drivers/gpu/drm/i915/gt/intel_workarounds.c

@@ -2000,6 +2000,7 @@ static const struct mcr_range mcr_ranges_xehp[] = {
 	{ .start =  0xdc00, .end =  0xffff },
 	{ .start = 0x17000, .end = 0x17fff },
 	{ .start = 0x24a00, .end = 0x24a7f },
+	{},
 };
 
 static bool mcr_range(struct drm_i915_private *i915, u32 offset)