drm/i915/bw: Fix num_planes handling on TGL+
The TGL+ bw code has an off by one error on the num_planes
calculation, and tgl_max_bw_index() incorrectly bumps
the num_planes to 1 from 0.
That approach made sense on ICL where num_planes is more or
less a minimum number of planes to consider for the group,
but on TGL+ num_planes really is a maximum number of planes,
so these adjustments no longer make any sense there.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260522200346.17377-2-ville.syrjala@linux.intel.com
Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>