drm: fix unsigned vs signed comparison issue in modeset ctl ioctl.

This fixes CVE-2011-1013.

Reported-by: Matthiew Herrb (OpenBSD X.org team)
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_irq.c

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 53120a7..28d1d3c 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1012,7 +1012,8 @@
 		    struct drm_file *file_priv)
 {
 	struct drm_modeset_ctl *modeset = data;
-	int crtc, ret = 0;
+	int ret = 0;
+	unsigned int crtc;
 
 	/* If drm_vblank_init() hasn't been called yet, just no-op */
 	if (!dev->num_crtcs)