Input: appletouch - fix DMA to/from stack buffer

CONFIG_DMA_API_DEBUG spotted an instance of appletouch using
an array on the stack as a DMA buffer for certain hardware.
Change it to use a kmalloc()ed buffer instead.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>