staging: exfat: remove the redundant check when kfree an object in exfat_destroy_inode

kfree has taken the null check in account. hence it is unnecessary to add the
null check before kfree the object. Just remove it.

Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Link: https://lore.kernel.org/r/1567591408-24268-1-git-send-email-zhongjiang@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>