bufferpool2: fix native handle race condition

Return cloned handle as output parameter in order to use it after
closing the bufferpool connection.

Bug: 138171841
Test: atest CtsMediaTestCases -- --module-arg CtsMediaTestCases:size:small
Merged-In: I4ac142fcb7e3ecdb3fb02792f516b343d71bfc38
Change-Id: I4ac142fcb7e3ecdb3fb02792f516b343d71bfc38
(cherry picked from commit dc5cb62f)