staging: comedi: comedi_test: use unsigned short for loopback values

The last sample values written to the AO subdevice channels by its
"insn_write" handler `waveform_ao_insn_write()` are stored in the member
array `ao_loopbacks[]` in the device private data `struct
waveform_private`.  They can be read back via the "insn_read" handler of
the AI subdevice `waveform_ai_insn_read()`.  As the stored sample values
are only 16 bits wide, change the type of the `ao_loopbacks[]` member to
`unsigned short` to save some space.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/comedi_test.c

@@ -70,7 +70,7 @@ struct waveform_private {
 	unsigned long state_bits;
 	unsigned int ai_scan_period;	/* AI scan period in usec */
 	unsigned int ai_convert_period;	/* AI conversion period in usec */
-	unsigned int ao_loopbacks[N_CHANS];
+	unsigned short ao_loopbacks[N_CHANS];
 };
 
 /* fake analog input ranges */