In btrfs_destroy_inode(), the variable root may be NULL, but the check
for this takes place after its value has already been dereferenced to
access its fs_info member. Move the dereference operation to later in
the function.
Fixes: a6dbd429d8dd ("Btrfs: fix panic when trying to destroy a newly allocated")
Addresses-Coverity: CID 1497103: Null pointer dereferences (REVERSE_INULL)
Signed-off-by: Alex Dewar <a.dewar@xxxxxxxxxxxx>