dmaengine: fsl-edma: fix channel parameter config for fixed channel requests

dmaengine: fsl-edma: fix channel parameter config for fixed channel requests

Configure only the requested channel when a fixed channel is specified
to avoid modifying other channels unintentionally.

Fix parameter configuration when a fixed DMA channel is requested on
i.MX9 AON domain and i.MX8QM/QXP/DXL platforms. When a client requests
a fixed channel (e.g., channel 6), the driver traverses channels 0-5
and may unintentionally modify their configuration if they are unused.

This leads to issues such as setting the `is_multi_fifo` flag unexpectedly,
causing memcpy tests to fail when using the dmatest tool.

Only affect edma memcpy test when the channel is fixed.

Fixes: 72f5801a4e2b ("dmaengine: fsl-edma: integrate v3 support")
Signed-off-by: Joy Zou <joy.zou@nxp.com>
Cc: stable@vger.kernel.org
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20250917-b4-edma-chanconf-v1-1-886486e02e91@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>