drm/i915/bios: drop the rest of the p_ prefixes from pointers

Not really kernel style, and sticks out like a sore thumb. No functional
changes.

Cc: Animesh Manna <animesh.manna@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/76b4f643e727bae39acd6f73d085f718eb012235.1503600621.git.jani.nikula@intel.com