mwifiex: Do not kfree cmd buf while unregistering PCIe

All the command buffers are freed in mwifiex_free_cmd_buffer()
and hence there is no need to kfree the current command buffer
again. This might ends up freeing memory allocated by some other
kernel code.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>