qseecom: return app_id correctly when looking up and loading app

When __qseecom_check_app_exsits() and __qseecom_load_fw() get app_id
from TZ, they save it to function's return value then return back.
But "app_id" is of type uint32, "ret" is int32, this will return
incorrect app_id to the caller if app_id is larger than 0x7FFFFFFF.
Thus make change to return app_id correctly.

Change-Id: I2ef98d64490c480d5416ee24ec6ca9aca9c8ca8a
Signed-off-by: Zhen Kong <zkong@codeaurora.org>