drm/i915/cnl: make function cnl_ddi_dp_set_dpll_hw_state static

The function cnl_ddi_dp_set_dpll_hw_state does not need to be in global
scope, so make it static.

Cleans up sparse warning:
"symbol 'cnl_ddi_dp_set_dpll_hw_state' was not declared. Should it
 be static?"
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170613134751.29196-1-colin.king@canonical.comReviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/intel_dpll_mgr.c

@@ -2292,8 +2292,9 @@ static bool cnl_ddi_hdmi_pll_dividers(struct intel_crtc *crtc,
 	return true;
 }
 
-bool cnl_ddi_dp_set_dpll_hw_state(int clock,
-				  struct intel_dpll_hw_state *dpll_hw_state)
+static bool
+cnl_ddi_dp_set_dpll_hw_state(int clock,
+			     struct intel_dpll_hw_state *dpll_hw_state)
 {
 	uint32_t cfgcr0;