dmaengine: stm32-mdma: fix chan initialization in stm32_mdma_irq_handler()

The parameter to pass back to the handler function when irq has been
requested is a struct stm32_mdma_device pointer, not a struct
stm32_mdma_chan pointer.
Even if chan is reinit later in the function, remove this wrong
initialization.

Fixes: a4ffb13c

 ("dmaengine: Add STM32 MDMA driver")
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20220504155322.121431-3-amelie.delaunay@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>