drivers: dma: stm32: the source and destination sizes must only match in v1

Commit e7f222a fixed the bug where a data size mismatch produces unexpected
behavior with the DMA on V1 devices. However, this limitation is only valid
for the STM32 series with V1 DMA, V2 doesn't have this. The STM32CubeMX
configuration tool correctly implements this limitation in the UI,
it is a good way to cross-check.

Signed-off-by: Benedek Kupper <kupper.benedek@gmail.com>