'skb' is allocated in digital_in_send_sdd_req(), but not free when
digital_in_send_cmd() failed, which will cause memory leak. Fix it
by freeing 'skb' if digital_in_send_cmd() return failed.

Fixes: 2c66daec ("NFC Digital: Add NFC-A technology support")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>