test_firmware: fix a memory leak bug

In test_firmware_init(), the buffer pointed to by the global pointer
'test_fw_config' is allocated through kzalloc(). Then, the buffer is
initialized in __test_firmware_config_init(). In the case that the
initialization fails, the following execution in test_firmware_init() needs
to be terminated with an error code returned to indicate this failure.
However, the allocated buffer is not freed on this execution path, leading
to a memory leak bug.

To fix the above issue, free the allocated buffer before returning from
test_firmware_init().

Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu>
Link: https://lore.kernel.org/r/1563084696-6865-1-git-send-email-wang6495@umn.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>