exfat: fix possible memory leak in exfat_find()

'es' is malloced from exfat_get_dentry_set() in exfat_find() and should
be freed before leaving from the error handling cases, otherwise it will
cause memory leak.

Fixes: 5f2aa075 ("exfat: add inode operations")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>