drm/i915: Rename variables in ilk_intermedidate_wm()

ilk_compute_intermediate_wm() uses rather poor variable names
for its watermark structs. Borrow a better naming convention
from the g4x/vlv counterpart code.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240916162413.8555-8-ville.syrjala@linux.intel.com


Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>