Get UID from list using stt_config_client_s structure

Get UID from list using stt_config_client_s structure

Current code converts the type of element as integer. However, the element of the list is instance
of stt_config_client_s structure. Because the first member of the structure is uid, so current code
has no problem until now. But this can occur problem if the type of uid or the order of member is
changed.

To solve this problem, this patch changes the type from integer to the structure. This can provide
safe access to member.

Change-Id: Ica103855b96bfc4196044772343216f75d38f9c0
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>