remoteproc: pull in slab.h

In preparation to virtio header changes, include slab.h directly as
this module is using it.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/remoteproc_sysfs.c

@@ -4,6 +4,7 @@
  */
 
 #include <linux/remoteproc.h>
+#include <linux/slab.h>
 
 #include "remoteproc_internal.h"