i915, debugfs: Fix uninitialized warning

gcc complains that:

drivers/gpu/drm/i915/i915_debugfs.c: In function ‘display_crc_ctl_write’:
drivers/gpu/drm/i915/i915_debugfs.c:2393:2: warning: ‘val’ may be used uninitialized in this function [-Wuninitialized]
drivers/gpu/drm/i915/i915_debugfs.c:2350:6: note: ‘val’ was declared here

but it can't see that we're going to use val only in the success case.
So shut it up.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2349,7 +2349,7 @@ static int pipe_crc_set_source(struct drm_device *dev, enum pipe pipe,
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_pipe_crc *pipe_crc = &dev_priv->pipe_crc[pipe];
-	u32 val;
+	u32 val = 0; /* shut up gcc */
 	int ret;
 
 	if (pipe_crc->source == source)