drm/i915: Remove the 'reg' local variable

Get rid of the local 'reg' variable for the DPLL control register
in i9xx_enable_pll(). We have other registers in there too so this
is just making things more confusing.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210715093530.31711-8-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>