Revert "block: split .sysfs_lock into two locks"

This reverts commit fa137b50.

It breaks the abi and is not needed in Android devices.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ia9b92ae9b03e3e12b13584373448160c767bf4cb