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>
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index fe29aad..348843b 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1101,7 +1101,7 @@
 	struct platform_device *platformdev; /**< Platform device struture */
 
 	struct drm_sg_mem *sg;	/**< Scatter gather memory */
-	int num_crtcs;                  /**< Number of CRTCs on this device */
+	unsigned int num_crtcs;                  /**< Number of CRTCs on this device */
 	void *dev_private;		/**< device private data */
 	void *mm_private;
 	struct address_space *dev_mapping;