arm64: kfence: fix header inclusion

Randconfig builds started warning about a missing function declaration
after set_memory_valid() is moved to a new file:

In file included from mm/kfence/core.c:26:
arch/arm64/include/asm/kfence.h:17:2: error: implicit declaration of function 'set_memory_valid' [-Werror,-Wimplicit-function-declaration]

Include the correct header again.

Link: https://lkml.kernel.org/r/20210125125025.102381-1-arnd@kernel.org
Fixes: 9e18ec3cfabd ("set_memory: allow querying whether set_direct_map_*() is actually enabled")
Fixes: 204555ff8bd6 ("arm64, kfence: enable KFENCE for ARM64")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

arch/arm64/include/asm/kfence.h

@@ -8,7 +8,7 @@
 #ifndef __ASM_KFENCE_H
 #define __ASM_KFENCE_H
 
-#include <asm/cacheflush.h>
+#include <asm/set_memory.h>
 
 static inline bool arch_kfence_init_pool(void) { return true; }