mdadm: Fix Segmentation fault.
In function write_init_super1():
If "rv = store_super1(st, di->fd)" return error and the di is the last.
Then the di = NULL && rv > 0, so exec:
if (rv)
fprintf(stderr, Name ": Failed to write metadata to%s\n",
di->devname);
will be segmentation fault.
Signed-off-by: majianpeng <majianpeng@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>