Ensure buffer data is 1-dimensional bytes

cast doesn't exist under Python 2, but that's okay - we'll just throw an
error (which we need to do anyway given the data isn't 1-D bytes). Under
Python 3, it'll attempt to cast but may fail if the data isn't
C-contiguous (again, that's okay)

picamera/mmalobj.py

@@ -1106,6 +1106,8 @@ def update(self, data):
             Some buffer objects *cannot* be modified without consequence (for
             example, buffers returned by an encoder's output port).
         """
+        if isinstance(data, memoryview) and (data.ndim > 1 or data.itemsize > 1):
+            data = data.cast('B')
         bp = ct.c_uint8 * len(data)
         try:
             sp = bp.from_buffer(data)