drivers: isdn: use kernel macros to convert hex digit

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Karsten Keil <isdn@linux-pingi.de>
Cc: Tilman Schmidt <tilman@imap.cc>
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/isdn/capi/capidrv.c b/drivers/isdn/capi/capidrv.c
index bf55ed5..2978bda 100644
--- a/drivers/isdn/capi/capidrv.c
+++ b/drivers/isdn/capi/capidrv.c
@@ -1450,12 +1450,9 @@
     	}
 
 	for (p = data, end = data+len; p < end; p++) {
-		u8 w;
 		PUTBYTE_TO_STATUS(card, ' ');
-		w = (*p >> 4) & 0xf;
-		PUTBYTE_TO_STATUS(card, (w < 10) ? '0'+w : 'A'-10+w);
-		w = *p & 0xf;
-		PUTBYTE_TO_STATUS(card, (w < 10) ? '0'+w : 'A'-10+w);
+		PUTBYTE_TO_STATUS(card, hex_asc_hi(*p));
+		PUTBYTE_TO_STATUS(card, hex_asc_lo(*p));
 	}
 	PUTBYTE_TO_STATUS(card, '\n');