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

In the Linux kernel, the following vulnerability has been resolved:

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.