Bluetooth: Remove unnecessary NULL check before vfree()

Remove unnecessary NULL check which causes coccinelle warning:

net/bluetooth/coredump.c:104:2-7: WARNING: NULL check before some
freeing functions is not needed.

Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>