net: phy: cortina: Ensure memory allocated is freed

net: phy: cortina: Ensure memory allocated is freed

In cs4340_upload_firmware a buffer is allocated with malloc but this is
never freed. The pointer to this buffer, addr, is not even kept
unchanged. But in some cases addr is not a buffer allocated by malloc.
Introduce the use of another pointer to keep track of the buffer and to
know if it needs to be freed.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>