staging/xillybus: Handle OOM in xillybus_init()

alloc_workqueue() can fail and returns NULL in case of
OOM.
Handle this case and undo class_create().

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --cc drivers/staging/xillybus/xillybus_core.c
Simple merge