staging: most: aim-cdev: make syscall write accept buffers of arbitrary size

This patch allows to call the write() function for synchronous and
isochronous channels with buffers of any size. The AIM simply waits for
data to fill up the MOST buffer object according to the network interface
controller specification for streaming channels, before it submits the
buffer to the HDM.

The new behavior is backward compatible to the old applications, since
all known applications needed to fill the buffer completely anyway.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>