include/linux/firmware.h: Define COMEDI_RELEASE_FIRMWARE_NOWAIT(fw)

include/linux/firmware.h: Define COMEDI_RELEASE_FIRMWARE_NOWAIT(fw)

The version of request_firmware_nowait() that takes a gfp_t parameter
also expects its callback function to call release_firmware() to free
the firmware, otherwise there is a memory leak.  The older version of
request_firmware_nowait() doesn't want the callback function to free the
firmware.  Define the macro COMEDI_RELEASE_FIRMWARE_NOWAIT(fw) to be
used in the callback function instead of calling release_firmware(fw)
directly.  This does nothing for the older request_firmware_nowait()
API, but calls release_firmware(fw) for the newer
request_firmware_nowait() API.

Change the request_firmware_nowait callback function in the usbdux,
usbduxfast and usbduxsigma drivers to use
COMEDI_RELEASE_FIRMWARE_NOWAIT().

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>