uml: Fix build breakage after slab.h changes

We now have to to include linux/slab.h explicitly for kmalloc &
friends.  Files that build against host headers already get their
prototypes via um_malloc.h, linux/slab.h may even be unavailable.
Signed-off-by: NJan Kiszka <jan.kiszka@web.de>
Signed-off-by: NTejun Heo <tj@kernel.org>

arch/um/drivers/line.c

@@ -6,6 +6,7 @@
 #include "linux/irqreturn.h"
 #include "linux/kd.h"
 #include "linux/sched.h"
+#include "linux/slab.h"
 #include "chan_kern.h"
 #include "irq_kern.h"
 #include "irq_user.h"

arch/um/os-Linux/helper.c

@@ -8,7 +8,6 @@
 #include <errno.h>
 #include <sched.h>
 #include <linux/limits.h>
-#include <linux/slab.h>
 #include <sys/socket.h>
 #include <sys/wait.h>
 #include "kern_constants.h"