drm/i915/pxp: fix __le64 access to get rid of sparse warning

__le64 and friends should go through the cpu_to_* and *_to_cpu
accessors:

drivers/gpu/drm/i915/pxp/intel_pxp_huc.c:41:35: warning: incorrect type in assignment (different base types)
drivers/gpu/drm/i915/pxp/intel_pxp_huc.c:41:35:    expected restricted __le64 [assigned] [usertype] huc_base_address
drivers/gpu/drm/i915/pxp/intel_pxp_huc.c:41:35:    got unsigned long long [assigned] [usertype] huc_phys_addr

Cc: Tomas Winkler <tomas.winkler@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Tomas Winkler <tomas.winkler@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230207124026.2105442-4-jani.nikula@intel.com