drm/i915: Remove unused variable ret

This patch fixes below warnings reported by coccicheck

./drivers/gpu/drm/i915/i915_debugfs.c:789:5-8: Unneeded variable: "ret". Return "0" on line 1012
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1603937925-53176-1-git-send-email-zou_wei@huawei.com

drivers/gpu/drm/i915/i915_debugfs.c

@@ -784,7 +784,6 @@ static int i915_frequency_info(struct seq_file *m, void *unused)
 	struct intel_uncore *uncore = &dev_priv->uncore;
 	struct intel_rps *rps = &dev_priv->gt.rps;
 	intel_wakeref_t wakeref;
-	int ret = 0;
 
 	wakeref = intel_runtime_pm_get(&dev_priv->runtime_pm);
 
@@ -1007,7 +1006,7 @@ static int i915_frequency_info(struct seq_file *m, void *unused)
 	seq_printf(m, "Max pixel clock frequency: %d kHz\n", dev_priv->max_dotclk_freq);
 
 	intel_runtime_pm_put(&dev_priv->runtime_pm, wakeref);
-	return ret;
+	return 0;
 }
 
 static int i915_ring_freq_table(struct seq_file *m, void *unused)