dmaengine: stm32-mdma: memset stm32_mdma_chan_config struct before using it

dmaengine: stm32-mdma: memset stm32_mdma_chan_config struct before using it

New bool m2m_hw has been added at the end of stm32_mdma_chan_config struct
to support the STM32 DMA MDMA chaining.

m2m_hw is set true in stm32_mdma_slave_config() if peripheral_size is set,
but m2m_hw is never initialized false.

To ensure this case, and any further new update of the structure, memset it
to 0 before using it.

Fixes: 696874322771 ("dmaengine: stm32-mdma: add support to be triggered by STM32 DMA")
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20221017131413.202567-1-amelie.delaunay@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>