dcdbas: remove a redundant smi_data_buf_free in dcdbas_exit

smi_data_buf_free is called twice in current implementation.
The second call simply return because smi_data_buf is set to NULL in first call.
This patch removes the second smi_data_buf_free call.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>