Fix invalid indentation - extra whitespace before error directive which
is causing syntax error when no pkgconfig file for the DPDK is found and
RTE_SDK is not specified.
Fixes: d299106e8e31 ("examples/ipsec-secgw: add IPsec sample application")
Cc: stable@dpdk.org
Signed-off-by: Marcin Smoczynski <marcinx.smoczynski@intel.com>