drm/i915/selftests: avoid using uninitialized context

There is an error path in igt_ppgtt_alloc(), which leads
to ww object being passed down to i915_gem_ww_ctx_fini() without
initialization. Correct that by only putting ppgtt->vm and
returning early.

Fixes: 480ae79 ("drm/i915/selftests: Prepare gtt tests for obj->mm.lock removal")
Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-by: Mikolaj Wasiak <mikolaj.wasiak@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/iuaonpjc3rywmvhna6umjlvzilocn2uqsrxfxfob24e2taocbi@lkaivvfp4777

Author: KKaras169169

drivers/gpu/drm/i915/selftests/i915_gem_gtt.c

@@ -168,7 +168,7 @@ static int igt_ppgtt_alloc(void *arg)
 		return PTR_ERR(ppgtt);
 
 	if (!ppgtt->vm.allocate_va_range)
-		goto err_ppgtt_cleanup;
+		goto ppgtt_vm_put;
 
 	/*
 	 * While we only allocate the page tables here and so we could
@@ -236,7 +236,7 @@ static int igt_ppgtt_alloc(void *arg)
 			goto retry;
 	}
 	i915_gem_ww_ctx_fini(&ww);
-
+ppgtt_vm_put:
 	i915_vm_put(&ppgtt->vm);
 	return err;
 }