drm/i915: Un-invert {i9xx,i965}_error_mask()

Make life a bit more straightforward by removing the bitwise
not from {i9xx,i965}_error_mask() and instead do it when feeding
the value to gen2_error_init(). Make life a bit easier I think.

Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250217070047.953-8-ville.syrjala@linux.intel.com