msm: msm_bus: fix the memory leak issue

Client name allocated dynamically during the registration
is not freed at the time of unregistration. This is
leading to memory leak issue. This patch fixes the issue
by freeing up the client name during unregistartion time.

Change-Id: I0fe75ce71fdf0ee9a1268d52ac244047cc3413d7
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>