net: bna: use correct type specifications

addr and len are read with
sscanf(kern_buf, "%x:%x", &addr, &len);
and used as arguments for
bna_reg_offset_check.

So they have to be unsigned.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>