xfs_db: fix crc invalidation segfault

xfs_db: fix crc invalidation segfault

The nowrite_ops var is declared within nested block scope but used
outside that scope, causing xfs_db to crash while trying to defererence
the verify_write pointer. Fix it by lifting the declaration to the outer
scope, where it is accessed.

Fixes: b64af2c48220c8 ("xfs_db: add crc manipulation commands")
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>