staging: vt6656: sparse fixes: dpc.c missing dpc.h

sparse warnings
dpc.c:249:5: warning: symbol 'RXbBulkInProcessData' was not declared. Should it be static?
dpc.c:1295:6: warning: symbol 'RXvWorkItem' was not declared. Should it be static?
dpc.c:1321:6: warning: symbol 'RXvFreeRCB' was not declared. Should it be static?
dpc.c:1356:6: warning: symbol 'RXvMngWorkItem' was not declared. Should it be static?

Signed-off-by: Malcolm Priestley <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/vt6656/dpc.c

···
  *
  */
 
+#include "dpc.h"
 #include "device.h"
 #include "rxtx.h"
 #include "tether.h"