staging: dgnc: Fix included header from 'asm'

This commit fixes the checkpatch warning:

drivers/staging/dgnc/dgnc_neo.c:37:
    WARNING: Use #include <linux/io.h> instead of <asm/io.h>
Signed-off-by: Konrad Zapalowicz <bergo.torino@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/dgnc/dgnc_neo.c

@@ -34,7 +34,7 @@
 #include <linux/sched.h>	/* For jiffies, task states */
 #include <linux/interrupt.h>    /* For tasklet and interrupt structs/defines */
 #include <linux/delay.h>	/* For udelay */
-#include <asm/io.h>		/* For read[bwl]/write[bwl] */
+#include <linux/io.h>		/* For read[bwl]/write[bwl] */
 #include <linux/serial.h>	/* For struct async_serial */
 #include <linux/serial_reg.h>	/* For the various UART offsets */