qlcnic: potential NULL dereference in qlcnic_83xx_get_minidump_template()

If qlcnic_fw_cmd_get_minidump_temp() fails then "fw_dump->tmpl_hdr" is
NULL or possibly freed.  It can lead to an oops later.

Fixes: d01a6d3c

 ('qlcnic: Add support to enable capability to extend minidump for iSCSI')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>