staging: wilc1000: move 'aging_timer' static variable to wilc_priv struct

Moved 'aging_timer' to wilc_priv struct instead of having it as static
variable.
As 'aging_timer' is maintained for each interfaces so 'op_ifcs' check is
not required before the timer_setup() and del_timer_sync() call.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>