appletalk/ddp.c: Neaten checksum function

atalk_sum_partial can now use the rol16 function in bitops.h

Signed-off-by: Joe Perches <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/appletalk/ddp.c

···
 {
 	/* This ought to be unwrapped neatly. I'll trust gcc for now */
 	while (len--) {
-		sum += *data;
-		sum <<= 1;
-		if (sum & 0x10000) {
-			sum++;
-			sum &= 0xffff;
-		}
-		data++;
+		sum += *data++;
+		sum = rol16(sum, 1);
 	}
 	return sum;
 }