mwifiex: get rid of global user_rmmod flag

bus.remove() callback function is called when user removes this module
from kernel space or ejects the card from the slot. The driver handles
these 2 cases differently. Few commands (FUNC_SHUTDOWN etc.) are sent to
the firmware only for module unload case.

The variable 'user_rmmod' is used to distinguish between these two
scenarios.

This patch checks hardware status and get rid of global variable
user_rmmod.

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