omap2fb: Fix stack memory disclosure

Using [1] for static analysis I found that the OMAPFB_QUERY_PLANE,
OMAPFB_GET_COLOR_KEY, OMAPFB_GET_DISPLAY_INFO, and OMAPFB_GET_VRAM_INFO
cases could all leak uninitialized stack memory--either due to
uninitialized padding or 'reserved' fields.

Fix them by clearing the shared union used to store copied out data.

[1] https://github.com/vlad902/kernel-uninitialized-memory-checkerSigned-off-by: Vlad Tsyrklevich <vlad@tsyrklevich.net>
Reviewed-by: Kees Cook <keescook@chromium.org>
Fixes: b39a982d ("OMAP: DSS2: omapfb driver")
Cc: security@kernel.org
[b.zolnierkie: prefix patch subject with "omap2fb: "]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/omap2/omapfb/omapfb-ioctl.c

@@ -609,6 +609,8 @@ int omapfb_ioctl(struct fb_info *fbi, unsigned int cmd, unsigned long arg)
 
 	int r = 0;
 
+	memset(&p, 0, sizeof(p));
+
 	switch (cmd) {
 	case OMAPFB_SYNC_GFX:
 		DBG("ioctl SYNC_GFX\n");