i2c: imx: zero-initialize dma_slave_config for eDMA

i2c: imx: zero-initialize dma_slave_config for eDMA

commit 66d88e16f204 ("dmaengine: fsl-edma: read/write multiple registers
in cyclic transactions") causes fsl_edma_fill_tcd() to read
dst_port_window_size and src_port_window_size when building transfer
control descriptors.

Initialize the structure so unset fields are explicitly zero.

Fixes: 66d88e16f204 ("dmaengine: fsl-edma: read/write multiple registers in cyclic transactions")
Signed-off-by: Anthony Pighin <anthony.pighin@nokia.com>
Cc: <stable@vger.kernel.org> # v6.14+
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20260331182632.888110-1-anthony.pighin@nokia.com