scsi: ibmvfc: Free channel_setup_buf during device tear down

The buffer for negotiating channel setup is DMA allocated at device probe
time. However, the remove path fails to free this allocation which will
prevent the hypervisor from releasing the virtual device in the case of a
hotplug remove.

Fix this issue by freeing the buffer allocation in ibmvfc_free_mem().

Link: https://lore.kernel.org/r/20210311012212.428068-1-tyreld@linux.ibm.com
Fixes: e95eef3f

 ("scsi: ibmvfc: Implement channel enquiry and setup commands")
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>