drm/i915/dpio: s/VLV_PLL_DW9_BCAST/VLV_PCS_DW17_BCAST/

drm/i915/dpio: s/VLV_PLL_DW9_BCAST/VLV_PCS_DW17_BCAST/

VLV_PLL_DW9_BCAST is actually VLV_PCS_DW17_BCAST. The address
does kinda look like it goes to the PLL block on a first glance,
but broadcast is special and doesn't even exist for the PLL
(only PCS and TX have it).

The fact that we use a broadcast write here is a bit sketchy
IMO since we're now blasting the register to all PCS splines
across the whole PHY. So the PCS registers in the other channel
(ie. other pipe/port) will also be written. But I guess the
fact that we always write the same value should make this a nop
even if the other channel is already enabled (assuming the VBIOS/GOP
didn't screw up and use some other value...).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240422083457.23815-4-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>