drm/i915: add parentheses around PIXCLK_GATE definitions

By looking at the current way we're using these definitions I don't
think this commit will fix any bug, but programmers from the future
are evil and will certainly find ways to combine macro expansion with
operator precedence to introduce bugs that are hard to find.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -4395,8 +4395,8 @@
 
 /* LPT PIXCLK_GATE */
 #define PIXCLK_GATE			0xC6020
-#define  PIXCLK_GATE_UNGATE		1<<0
-#define  PIXCLK_GATE_GATE		0<<0
+#define  PIXCLK_GATE_UNGATE		(1<<0)
+#define  PIXCLK_GATE_GATE		(0<<0)
 
 /* SPLL */
 #define SPLL_CTL			0x46020