soc: microchip: mpfs: Fix memory leak in mpfs_sys_controller_probe()

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

soc: microchip: mpfs: Fix memory leak in mpfs_sys_controller_probe()

In mpfs_sys_controller_probe(), if of_get_mtd_device_by_node() fails,

the function returns immediately without freeing the allocated memory

for sys_controller, leading to a memory leak.

Fix this by jumping to the out_free label to ensure the memory is

properly freed.

Also, consolidate the error handling for the mbox_request_channel()

failure case to use the same label.