easy-setup: Fix Initialization warning (var is char not string)

easy-setup: Fix Initialization warning (var is char not string)

Observed issue was:

  service/easy-setup/sampleapp/enrollee/linux/enrolleewifi.c:262:19: \
  warning: initialization makes integer from pointer without a cast [enabled by default]
  char option = "";

Change-Id: Ib86e46094dee109a82cd483669480dbe97e8c570
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18329
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Alex Kelley <alexke@microsoft.com>
Reviewed-by: Heewon Park <h_w.park@samsung.com>
Reviewed-by: Jihun Ha <jihun.ha@samsung.com>
Reviewed-by: Uze Choi <uzchoi@samsung.com>