ieee802154: cc2520: Fix error return code in cc2520_hw_init()

In cc2520_hw_init(), if oscillator start failed, the error code
should be returned.

Fixes: 0da6bc8c

 ("ieee802154: cc2520: adds driver for TI CC2520 radio")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Link: https://lore.kernel.org/r/20221120075046.2213633-1-william.xuanziyang@huawei.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>