staging: comedi: adq12b: usleep_range is preferred over udelay

Fix checkpatch.pl issue:

CHECK: usleep_range is preferred over udelay; see
       Documentation/timers/timers-howto.txt

Replace the udelay() with usleep_range() with a reasonable upper limit.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/adq12b.c

@@ -129,7 +129,7 @@ static int adq12b_ai_insn_read(struct comedi_device *dev,
 	if (val != devpriv->last_ctreg) {
 		outb(val, dev->iobase + ADQ12B_CTREG);
 		devpriv->last_ctreg = val;
-		udelay(50);	/* wait for the mux to settle */
+		usleep_range(50, 100);	/* wait for the mux to settle */
 	}
 
 	val = inb(dev->iobase + ADQ12B_ADLOW);	/* trigger A/D */