drm/i915: Fix GPIO pin to register mapping

In i2c GPIO fallback, index 6 is reserved for nothing.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 2449a74..2be4f72 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -155,6 +155,7 @@
 		GPIOC,
 		GPIOD,
 		GPIOE,
+		0,
 		GPIOF,
 	};
 	struct intel_gpio *gpio;