drm/i915: Fix declaration of intel_gmbus_{is_forced_bit/is_port_falid}

Description:
intel_gmbus_is_forced_bit is no extern as its body is right below.
Likewise for intel_gmbus_is_port_valid.

This fixes a compilation issue with clang. An initial version of this patch
was developed by PaX Team <pageexec at freemail.hu>.
This is respin of this patch.

20130509: v2: (re-)add inline upon request.

Signed-off-by: Jan-Simon Möller <dl9pf@gmx.de>
CC: pageexec@freemail.hu
CC: daniel.vetter@ffwll.ch
CC: airlied@linux.ie
CC: intel-gfx@lists.freedesktop.org
CC: dri-devel@lists.freedesktop.org
CC: linux-kernel@vger.kernel.org
[danvet: Bikeshed commit message.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1809,7 +1809,7 @@ void i915_teardown_sysfs(struct drm_device *dev_priv);
 /* intel_i2c.c */
 extern int intel_setup_gmbus(struct drm_device *dev);
 extern void intel_teardown_gmbus(struct drm_device *dev);
-extern inline bool intel_gmbus_is_port_valid(unsigned port)
+static inline bool intel_gmbus_is_port_valid(unsigned port)
 {
 	return (port >= GMBUS_PORT_SSC && port <= GMBUS_PORT_DPD);
 }
@@ -1818,7 +1818,7 @@ extern struct i2c_adapter *intel_gmbus_get_adapter(
 		struct drm_i915_private *dev_priv, unsigned port);
 extern void intel_gmbus_set_speed(struct i2c_adapter *adapter, int speed);
 extern void intel_gmbus_force_bit(struct i2c_adapter *adapter, bool force_bit);
-extern inline bool intel_gmbus_is_forced_bit(struct i2c_adapter *adapter)
+static inline bool intel_gmbus_is_forced_bit(struct i2c_adapter *adapter)
 {
 	return container_of(adapter, struct intel_gmbus, adapter)->force_bit;
 }