msm: mdp: Fix reserved field usage

An earlier commit(ec5b2f)increased the number of reserved fields
in the kernel standard fb.h header changing the struct size.
This caused issues with userland applications using the corresponding
bionic header. This patch revert the earlier increas in size
and makes corresponding adjustments to the reserved field usage.
A follow up patch will remove usage of reserved fields entirely.
diff --git a/include/linux/fb.h b/include/linux/fb.h
index f6a2923..d31cb68 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -279,7 +279,7 @@
 	__u32 vmode;			/* see FB_VMODE_*		*/
 	__u32 rotate;			/* angle we rotate counter clockwise */
 	__u32 colorspace;		/* colorspace for FOURCC-based modes */
-	__u32 reserved[5];		/* Reserved for future compatibility */
+	__u32 reserved[4];		/* Reserved for future compatibility */
 };
 
 struct fb_cmap {