Allow multiple calls on OCResource::observe().

Allow multiple calls on OCResource::observe().

Remove check against m_observeHandle in OCResource::observe().
This will allow mutliple calls on observe with different query
parameters.

Bug: https://jira.iotivity.org/browse/IOT-1115
Change-Id: I1bae9e8db8999bf6e805eec75ebcbe9f4af8b3c7
Signed-off-by: Ziran Sun <ziran.sun@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11735
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Todd Malsbary <todd.malsbary@intel.com>
Reviewed-by: Habib Virji <habib.virji@samsung.com>
(cherry picked from commit 66b4b024a7d317913c377949d94a298a4a224c42)
Reviewed-on: https://gerrit.iotivity.org/gerrit/11993