drm/i915/cnl: Change the macro name to DPLL_CFGCR0_DCO_FRACTION_SHIFT

No functional changes. Only change the macro from
"DPLL_CFGCR0_DC0_FRAC_SHIFT to DPLL_CFGCR0_DCO_FRACTION_SHIFT
to be consistent with DPLL_CFGCR0_DCO_FRACTION_MASK
and DPLL_CFGCR0_DCO_FRACTION

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1505413899-30876-1-git-send-email-manasi.d.navare@intel.com