drm/i915/selftests: Initialise request to silence a compiler

With an old (4.7.3 on 32bit) gcc, it emits a warning for

In file included from drivers/gpu/drm/i915/i915_request.c:1425:0:
drivers/gpu/drm/i915/selftests/i915_request.c: In function ‘live_nop_request’:
drivers/gpu/drm/i915/selftests/i915_request.c:380:21: error: ‘request’ may be used uninitialized in this function [-Werror=maybe-uninitialized]

Silence it by just setting it to NULL on initialisation.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180614124923.18071-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/selftests/i915_request.c

@@ -342,9 +342,9 @@ static int live_nop_request(void *arg)
 	mutex_lock(&i915->drm.struct_mutex);
 
 	for_each_engine(engine, i915, id) {
-		IGT_TIMEOUT(end_time);
-		struct i915_request *request;
+		struct i915_request *request = NULL;
 		unsigned long n, prime;
+		IGT_TIMEOUT(end_time);
 		ktime_t times[2] = {};
 
 		err = begin_live_test(&t, i915, __func__, engine->name);