drivers/input/ff-core.c needs <linux/sched.h>

Commit 656acd2bbc4ce7f224de499ee255698701396c48 ("Input: fix locking in
force-feedback core") causes the following regression on m68k:

| linux/drivers/input/ff-core.c: In function 'input_ff_upload':
| linux/drivers/input/ff-core.c:172: error: dereferencing pointer to incomplete type
| linux/drivers/input/ff-core.c: In function 'erase_effect':
| linux/drivers/input/ff-core.c:197: error: dereferencing pointer to incomplete type
| linux/drivers/input/ff-core.c:204: error: dereferencing pointer to incomplete type
| make[4]: *** [drivers/input/ff-core.o] Error 1

As the incomplete type is `struct task_struct', including <linux/sched.h> fixes
it.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Dmitry Torokhov <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/input/ff-core.c

···
 #include <linux/input.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/sched.h>
 
 /*
  * Check that the effect_id is a valid effect and whether the user