drm/i915: Mark the static key for movntqda as static

Silence sparse who warns that the global variable is not declared
static.

Fixes: 0b1de5d58e19 ("drm/i915: Use SSE4.1 movntdqa to ...")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Akash Goel <akash.goel@intel.com>
Cc: Damien Lespiau <damien.lespiau@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471432146-5196-1-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/i915_memcpy.c

@@ -27,7 +27,7 @@
 
 #include "i915_drv.h"
 
-DEFINE_STATIC_KEY_FALSE(has_movntdqa);
+static DEFINE_STATIC_KEY_FALSE(has_movntdqa);
 
 #ifdef CONFIG_AS_MOVNTDQA
 static void __memcpy_ntdqa(void *dst, const void *src, unsigned long len)