kasan: fix build by including kernel.h

The <linux/kasan.h> header relies on _RET_IP_ being defined, and had been
receiving that definition via inclusion of bug.h which includes kernel.h.
However, since f39650de687e ("kernel.h: split out panic and oops helpers")
that is no longer the case and get the following build error when building
CONFIG_KASAN_HW_TAGS on arm64:

In file included from arch/arm64/mm/kasan_init.c:10:
include/linux/kasan.h: In function 'kasan_slab_free':
include/linux/kasan.h:230:39: error: '_RET_IP_' undeclared (first use in this function)
230 | return __kasan_slab_free(s, object, _RET_IP_, init);

Fix it by including kernel.h from kasan.h.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: f39650de687e ("kernel.h: split out panic and oops helpers")
Signed-off-by: Marco Elver <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Andrey Konovalov <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Peter Collingbourne <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Vincenzo Frascino <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/kasan.h

···
 #define _LINUX_KASAN_H
 
 #include <linux/bug.h>
+#include <linux/kernel.h>
 #include <linux/static_key.h>
 #include <linux/types.h>