The recent changes in 4.9 to mandate USB buffers be heap allocated
broke this driver, which was allocating the buffers on the stack.
This resulted in the device failing at initialization.

Introduce dedicated send/receive buffers as part of the state
structure, and add a mutex to protect access to them.

Note: we also had to tweak the API to mxl111sf_ctrl_msg to pass
the pointer to the state struct rather than the device, since
we need it inside the function to access the buffers and the
mutex.  This patch adjusts the callers to match the API change.
Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Reported-by: Doug Lung <dlung0@gmail.com>
Cc: Michael Ira Krufky <mkrufky@linuxtv.org>
Cc: <stable@vger.kernel.org>      # for v4.5 and up
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>