dmaengine: qcom: gpi: Fix memory leak in gpi_peripheral_config()

dmaengine: qcom: gpi: Fix memory leak in gpi_peripheral_config()

Fix a memory leak in gpi_peripheral_config() where the original memory
pointed to by gchan->config could be lost if krealloc() fails.

The issue occurs when:
1. gchan->config points to previously allocated memory
2. krealloc() fails and returns NULL
3. The function directly assigns NULL to gchan->config, losing the
   reference to the original memory
4. The original memory becomes unreachable and cannot be freed

Fix this by using a temporary variable to hold the krealloc() result
and only updating gchan->config when the allocation succeeds.

Found via static analysis and code review.

Fixes: 5d0c3533a19f ("dmaengine: qcom: Add GPI dma driver")
Cc: stable@vger.kernel.org
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Link: https://patch.msgid.link/20251029123421.91973-1-linmq006@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>