drm/i915: Sanitize the display fused-off check on GEN7/8

Detecting in intel_device_info_runtime_init() that the display is fused
off or not present should only zero intel_runtime_info::pipe_mask, while
the other related masks will be accordingly zeroed later in the
function. Remove the redundant zeroing of the related fields on GEN7/8.

Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230208114300.3123934-5-imre.deak@intel.com