video: fbdev: udlfb: Fix buffer on stack

Allocate buffers on HEAP instead of STACK for local array
that is to be sent using usb_control_msg().

Signed-off-by: Maksim Salau <maksim.salau@gmail.com>
Cc: Bernie Thompson <bernie@plugable.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>