Revert "spi: fix use-after-free of the add_lock mutex"

This reverts commit 11eab327 which is
commit 6c53b45c 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: I12195be6d1212c00e0d1a80aa3feddcb01bb7dbe
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>