staging: comedi: das1800: change type of 'ai_speed' boardinfo

This value is compared against the unsigned int cmd->convert_arg to
check the minimum value (max speed) for the analog input conversion
timing.

For aesthetics, change the type to match the cmd->convert_arg type.
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/das1800.c

@@ -225,7 +225,7 @@ enum das1800_boardid {
 struct das1800_board {
 	const char *name;
 	unsigned char id;
-	int ai_speed;		/* max conversion period in nanoseconds */
+	unsigned int ai_speed;
 	unsigned int is_01_series:1;
 };