i2400m: drop i2400m_schedule_work()

i2400m implements dynamic work allocation and queueing mechanism in
i2400_schedule_work(); however, this is only used for reset and
recovery which can be served equally well with preallocated per device
works.

Replace i2400m_schedule_work() with two work structs in struct i2400m.
These works are explicitly canceled when the device is released making
calls to flush_scheduled_work(), which is being deprecated,
unnecessary.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
Cc: linux-wimax@intel.com
Cc: netdev@vger.kernel.org