fbdev: shmobile: fix snprintf truncation

The name of the overlay does not fit into the fixed-length field:

drivers/video/fbdev/sh_mobile_lcdcfb.c:1577:2: error: 'snprintf' will always be truncated; specified size is 16, but format string expands to at least 25

Make it short enough by changing the string.

Fixes: c5deac3c ("fbdev: sh_mobile_lcdc: Implement overlays support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Helge Deller <deller@gmx.de>