mwifiex: mwifiex_unmap_pci_memory() handling for sleep confirm

Sleep confirm is a special command for which "adapter->cur_cmd" pointer
is not set. When it's response is received, host writes SLEEP confirm done
to a register. Firmware will perform DMA for writing sleep cookie signature
on same buffer after this.

Let's not immediately call mwifiex_unmap_pci_memory() for this special
command. Unmapping will be done when firmware completes writing sleep
cookie signature.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>