staging: comedi: das08: rename and rewrite DAS08_IRQ

The `DAS08_IRQ` macro contains a mask for the "IRQ" status bit.  This is
set to 1 when a rising edge is detected on the external interrupt input
pin of the external connector (which may be jumpered to a pacer output).
It is cleared by setting the "INTE" control bit to 0.  It is not used on
"JR" boards.  Rename the macro to `DAS08_STATUS_IRQ` and add a comment.
Also use the `BIT()` macro to define the value.
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/das08.c

@@ -59,7 +59,12 @@
 #define DAS08_AI_TRIG_REG	0x01	/* (W) AI software trigger */
 #define DAS08_STATUS_REG	0x02	/* (R) status */
 #define DAS08_STATUS_AI_BUSY	BIT(7)	/* AI conversion in progress */
-#define   DAS08_IRQ			(1<<3)
+/*
+ * The IRQ status bit is set to 1 by a rising edge on the external interrupt
+ * input (which may be jumpered to the pacer output).  It is cleared by
+ * setting the INTE control bit to 0.  Not present on "JR" boards.
+ */
+#define DAS08_STATUS_IRQ	BIT(3)	/* latched interrupt input */
 #define   DAS08_IP(x)			(((x)>>4)&0x7)
 #define DAS08_CONTROL		2
 #define   DAS08_MUX_MASK	0x7