mwifiex: correction in wakeup timer handling

Wakeup timer is in sync with 'pm_wakeup_fw_try' flag. It
has been started instead of cancelling at one place. This
patch corrects it.

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