disable debugging version of write_lock()

We've confirmed that the debug version of write_lock() can get stuck for long
enough to cause NMI watchdog timeouts and hence a crash.

We don't know why, yet.   Disable it for now.

Also disable the similar read_lock() code.  Just in case.

Thanks to Dave Olson <olson@unixfolk.com> for reporting and testing.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>