bt-api: gatt-client: Fix memory leak

bt-api: gatt-client: Fix memory leak

[Model]COMMON
[BinType] AP
[Customer]N/A

[Issue#]Memeory leak reported by cppcheck automated tool
[Request]Internal
[Occurrence Version]PK6

[Problem]Memeory leak reported by cppcheck tool
[Cause & Measure]We were no freeing the memory
[Checking Method]Gatt test tool

[Team]BT
[Developer]Syam Sidhardhan <s.syam@samsung.com>
[Solution company] Samsung
[Change Type]N/A

Change-Id: I2002d1f47cc3381a7db442cb72e3880af1a09aac
(cherry picked from commit 24374850100b737a9132c7b02a61955aed97326f)