staging: comedi: usbduxsigma: fix sparse endianness warnings

Sparse has many warnings like:

drivers/staging/comedi/drivers/usbduxsigma.c:293:21: warning: cast to
restricted __be32

on lines on which devpriv->in_buf is passed to be32_to_cpu().  This
suggests that this variable should actually be of type __be32.
Signed-off-by: Chase Southwood <chase.southwood@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbduxsigma.c

@@ -155,7 +155,7 @@ struct usbduxsigma_private {
 	/* size of the PWM buffer which holds the bit pattern */
 	int pwm_buf_sz;
 	/* input buffer for the ISO-transfer */
-	uint32_t *in_buf;
+	__be32 *in_buf;
 	/* input buffer for single insn */
 	uint8_t *insn_buf;