netxen_nic: signedness bug in netxen_md_entry_err_chk()

"esize" should be signed because it can be negative here.  For example,
when we call it in netxen_parse_md_template(), it could be -1 from the
return value of netxen_md_L2Cache().

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>