Fix ISDN/Gigaset build failure

Commit b91ecb00 ("gigaset: include cleanup cleanup") removed an implicit
sched.h inclusion that came in via slab.h, and caused various compile
problems as a result.

This should fix it.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/isdn/gigaset/gigaset.h b/drivers/isdn/gigaset/gigaset.h
index d32efb6..05947f9 100644
--- a/drivers/isdn/gigaset/gigaset.h
+++ b/drivers/isdn/gigaset/gigaset.h
@@ -20,6 +20,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/kernel.h>
+#include <linux/sched.h>
 #include <linux/compiler.h>
 #include <linux/types.h>
 #include <linux/ctype.h>