smb/client: Prevent error pointer dereference

smb/client: Prevent error pointer dereference

The cifs_sb_tlink() function can return error pointers, but this code
dereferences it before checking for error pointers.  Re-order the code
to fix that.

Fixes: 0f9b6b045bb2 ("fs/smb/client: implement chmod() for SMB3 POSIX Extensions")
Signed-off-by: Dan Carpenter <[email protected]>
Reviewed-by: Bharath SM <[email protected]>
Signed-off-by: Steve French <[email protected]>