qseecom: fix listener unregistration issue

When listener unregister thread wakes up due to some system signals,
but not because ioctl_cnt <=1, it should return directly, instead of
continuing to remove listener list entry, which will lead kernel panic
when another listener receive thread accesses this freed entry.

Change-Id: I6ff97c56867d008232d7c50b22b372b0856c8dff
Signed-off-by: Zhen Kong <zkong@codeaurora.org>