drm/i915: fix driver's versions of WARN_ON & WARN_ON_ONCE

The current versions of these two macros don't work correctly if the
argument expression happens to contain a modulo operator (%) -- when
stringified, it gets interpreted as a printf formatting character!
With a specifically crafted parameter, this could probably cause a
kernel OOPS; consider WARN_ON(p%s) or WARN_ON(f %*pEp).

Instead, we should use an explicit "%s" format, with the stringified
expression as the coresponding literal-string argument.
Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -68,11 +68,11 @@
 		BUILD_BUG_ON(__i915_warn_cond); \
 	WARN(__i915_warn_cond, "WARN_ON(" #x ")"); })
 #else
-#define WARN_ON(x) WARN((x), "WARN_ON(" #x ")")
+#define WARN_ON(x) WARN((x), "WARN_ON(%s)", #x )
 #endif
 
 #undef WARN_ON_ONCE
-#define WARN_ON_ONCE(x) WARN_ONCE((x), "WARN_ON_ONCE(" #x ")")
+#define WARN_ON_ONCE(x) WARN_ONCE((x), "WARN_ON_ONCE(%s)", #x )
 
 #define MISSING_CASE(x) WARN(1, "Missing switch case (%lu) in %s\n", \
 			     (long) (x), __func__);