sh: fix uninitialized spinlock

The spinlock in traps_64.c is used without initialization.
This fixes it by declaring DEFINE_SPINLOCK() and makes the spinlock static
variable.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: linux-sh@vger.kernel.org
Signed-off-by: Paul Mundt <lethal@linux-sh.org>