drm/i915: Convert EFAULT into a silent SIGBUS

EFAULT will be a possible return code where backing storage is
transient, such after it is purged by madvise. As such it is to be
expected and so should not trigger a WARN inside i915_gem_fault() but be
converted silently to SIGBUS.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -1453,6 +1453,7 @@ out:
 		ret = VM_FAULT_OOM;
 		break;
 	case -ENOSPC:
+	case -EFAULT:
 		ret = VM_FAULT_SIGBUS;
 		break;
 	default: