btrfs.c: cleanup use of tcp->auxstr
btrfs.c: cleanup use of tcp->auxstr

* btrfs.c (btrfs_ioctl): Reset tcp->auxstr only if it is set.

Saruta/strace,cuviper/strace,Saruta/strace,Saruta/strace,Saruta/strace,cuviper/strace,Saruta/strace,cuviper/strace,cuviper/strace,cuviper/strace