drm/i915: add braces around KHz/MHz macro parameters

It's an accident waiting to happen.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_drv.h

@@ -65,8 +65,8 @@
 #define wait_for_atomic_us(COND, US) _wait_for((COND), \
 					       DIV_ROUND_UP((US), 1000), 0)
 
-#define KHz(x) (1000*x)
-#define MHz(x) KHz(1000*x)
+#define KHz(x) (1000 * (x))
+#define MHz(x) KHz(1000 * (x))
 
 /*
  * Display related stuff