drm/i915/tgl: Fix doc not corresponding to code

Replace PLLs names used in documentation to that used in the code.

Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Fixes: 68ff39c3 ("drm/i915/tgl: Add new pll ids")
Signed-off-by: Anna Karas <anna.karas@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190926123559.15717-1-anna.karas@intel.com