fbdev: fbmem: fix memory access if logo is bigger than the screen

There is no clipping on the x or y axis for logos larger that the framebuffer
size. Therefore: a logo bigger than screen size leads to invalid memory access:

[    1.254664] Backtrace:
[    1.254728] [<c02714e0>] (cfb_imageblit) from [<c026184c>] (fb_show_logo+0x620/0x684)
[    1.254763]  r10:00000003 r9:00027fd8 r8:c6a40000 r7:c6a36e50 r6:00000000 r5:c06b81e4
[    1.254774]  r4:c6a3e800
[    1.254810] [<c026122c>] (fb_show_logo) from [<c026c1e4>] (fbcon_switch+0x3fc/0x46c)
[    1.254842]  r10:c6a3e824 r9:c6a3e800 r8:00000000 r7:c6a0c000 r6:c070b014 r5:c6a3e800
[    1.254852]  r4:c6808c00
[    1.254889] [<c026bde8>] (fbcon_switch) from [<c029c8f8>] (redraw_screen+0xf0/0x1e8)
[    1.254918]  r10:00000000 r9:00000000 r8:00000000 r7:00000000 r6:c070d5a0 r5:00000080
[    1.254928]  r4:c6808c00
[    1.254961] [<c029c808>] (redraw_screen) from [<c029d264>] (do_bind_con_driver+0x194/0x2e4)
[    1.254991]  r9:00000000 r8:00000000 r7:00000014 r6:c070d5a0 r5:c070d5a0 r4:c070d5a0

So prevent displaying a logo bigger than screen size and avoid invalid
memory access.
Signed-off-by: Manfred Schlaegl <manfred.schlaegl@ginzinger.com>
Signed-off-by: Martin Kepplinger <martin.kepplinger@ginzinger.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/core/fbmem.c

@@ -431,6 +431,9 @@ static void fb_do_show_logo(struct fb_info *info, struct fb_image *image,
 {
 	unsigned int x;
 
+	if (image->width > info->var.xres || image->height > info->var.yres)
+		return;
+
 	if (rotate == FB_ROTATE_UR) {
 		for (x = 0;
 		     x < num && image->dx + image->width <= info->var.xres;