Correct missuse of get attribute value in ResourceClient unit test.

Correct missuse of get attribute value in ResourceClient unit test.

Change-Id: I57863e2291451aea5f1ce6d5fb7059b29d68a102
Signed-off-by: Ziran Sun <ziran.sun@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/14847
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: JungYong KIM <jyong2.kim@samsung.com>
(cherry picked from commit 9146a47b8249bda1f62a45592d81dde47dcb2942)
Reviewed-on: https://gerrit.iotivity.org/gerrit/14875
Reviewed-by: Uze Choi <uzchoi@samsung.com>