niu: Fix unused variable warning.

Don't strain gcc's tiny mind.

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

drivers/net/niu.c

···
 {
 	u64 val = 0;
 
+	*ret = 0;
 	switch (rp->rbr_block_size) {
 	case 4 * 1024:
 		val |= (RBR_BLKSIZE_4K << RBR_CFIG_B_BLKSIZE_SHIFT);