Staging: comedi: comedi_test.c should include timer.h

Fix this build error:
.../comedi_test.c:82: error: field timer has incomplete type
.../comedi_test.c: In function waveform_ai_interrupt:
.../comedi_test.c:188: error: implicit declaration of function mod_timer
.../comedi_test.c:188: error: jiffies undeclared (first use in this function)

Signed-off-by: Alexander Beregalov <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/comedi/drivers/comedi_test.c

···
 #include <asm/div64.h>
 
 #include "comedi_fc.h"
+#include <linux/timer.h>
 
 /* Board descriptions */
 struct waveform_board {