net: bna: use correct type specifier (2)

add and val are read with
sscanf(kern_buf, "%x:%x", &addr, &val);
and used as arguments for bna_reg_offset_check and writel
so they have to be unsigned.

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