Revert "Bluetooth: hci_sync: Fix overwriting request callback"

This reverts commit da77c1d3 which is
commit 2615fd9a upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I4250b5552873f25a1a0dec32159511eeb96aac9a
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>