mm, zsmalloc: Convert zsmalloc_handle.lock to spinlock_t

local_lock_t becoming a synonym of spinlock_t had consequences for the RT
mods to zsmalloc, which were taking a mutex while holding a local_lock,
inspiring a lockdep "BUG: Invalid wait context" gripe.

Converting zsmalloc_handle.lock to a spinlock_t restored lockdep silence.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>