drivers: udc_dwc2: Allocate multiple of bMaxPacketSize0

Control OUT buffers must be multiple of bMaxPacketSize0 in Buffer DMA
mode. While the transfer can be configured to smaller values, DMA will
write data past the buffer (and transfer size counter will underflow) if
the packet on the bus is larger or if there are multiple back-to-back
SETUP packets.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>