USB: mos7720: fix DMA to stack

commit 72ea18a558ed7a63a50bb121ba60d73b5b38ae30 upstream.

The read_mos_reg function is called with stack-allocated buffers, which
must not be used for control messages.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>