v4l2_frmsize_stepwise structure contains misnamed member

[Justin Gottula]

v4l2.py has the following definition for the `v4l2_frmsize_stepwise` structure:

  class v4l2_frmsize_stepwise(ctypes.Structure):
      _fields_ = [
          ('min_width', ctypes.c_uint32),
          ('min_height', ctypes.c_uint32),
          ('step_width', ctypes.c_uint32),
          ('min_height', ctypes.c_uint32),
          ('max_height', ctypes.c_uint32),
          ('step_height', ctypes.c_uint32),
      ]

But the authoritative upstream C headers (see: https://git.linuxtv.org/v4l-utils.git/tree/include/linux/videodev2.h?id=v4l-utils-1.14.2#n724) have the definition for the same structure as follows:

  struct v4l2_frmsize_stepwise {
          __u32 min_width; /* Minimum frame width [pixel] */
          __u32 max_width; /* Maximum frame width [pixel] */
          __u32 step_width; /* Frame width step size [pixel] */
          __u32 min_height; /* Minimum frame height [pixel] */
          __u32 max_height; /* Maximum frame height [pixel] */
          __u32 step_height; /* Frame height step size [pixel] */
  };

Notice that the second member is supposed to be named `max_width`; not `min_height`. Also notice that in the Python structure definition, there are TWO members named `min_height` in the same structure!

This means that
(a) it's unclear whether accessing `min_height` via python-v4l2 will access the correct member; and
(b) it's impossible to actually access the `max_width` member via python-v4l2; and
(c) the python-v4l2 code here is obviously just wrong, relative to the C v4l2 headers.

So in summary: the Python structure definition for `v4l2_frmsize_stepwise` needs to be corrected to use the correct name `max_width` for its second member. I've attached a one-liner patch that applies the necessary fix.