drm/i915/display: Bitwise or the conversion colour specifier together

drivers/gpu/drm/i915/display/intel_dp.c:6922 intel_dp_update_420() warn: should this be a bitwise op?
drivers/gpu/drm/i915/display/intel_dp.c:6922 intel_dp_update_420() warn: should this be a bitwise op?
drivers/gpu/drm/i915/display/intel_dp.c:6923 intel_dp_update_420() warn: should this be a bitwise op?

Inside drm_dp_downstream_rgb_to_ycbcr_conversion(), that parameter
'color_spc' is used as return port_cap[3] & color_spc, implying that it
is indeed a mask and not a boolean value.

Fixes: 522508b6 ("drm/i915/display: Let PCON convert from RGB to YCbCr if it can")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201223103917.14687-1-chris@chris-wilson.co.uk