transport: Handle SCMI payload size error

The transport module is responsible for managing the SCMI message header functionality, which includes checking the size of the command payload and copying the payload. If the reported size exceeds the command buffer size, the platform should respond with an error and exit the function without further command processing. However, the current implementation checks the size and reports the error but fails to exit the function. Instead, it continues copying and processing the command, leading to a buffer overflow by overwriting the SCP internal memory. This change will ensure the command handling terminates correctly by exiting the function.

Signed-off-by: Tarek El-Sherbiny tarek.el-sherbiny@arm.com