livepatch: make klp_mutex proper part of API

klp_mutex is shared between core.c and transition.c, and as such would
rather be properly located in a header so that we don't have to play
'extern' games from .c sources.

This also silences sparse warning (wrongly) suggesting that klp_mutex
should be defined static.
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

kernel/livepatch/core.c

@@ -31,6 +31,7 @@
 #include <linux/moduleloader.h>
 #include <linux/completion.h>
 #include <asm/cacheflush.h>
+#include "core.h"
 #include "patch.h"
 #include "transition.h"
 

kernel/livepatch/core.h

+#ifndef _LIVEPATCH_CORE_H
+#define _LIVEPATCH_CORE_H
+
+extern struct mutex klp_mutex;
+
+#endif /* _LIVEPATCH_CORE_H */

kernel/livepatch/transition.c

@@ -21,6 +21,7 @@
 
 #include <linux/cpu.h>
 #include <linux/stacktrace.h>
+#include "core.h"
 #include "patch.h"
 #include "transition.h"
 #include "../sched/sched.h"
@@ -28,8 +29,6 @@
 #define MAX_STACK_ENTRIES  100
 #define STACK_ERR_BUF_SIZE 128
 
-extern struct mutex klp_mutex;
-
 struct klp_patch *klp_transition_patch;
 
 static int klp_target_state = KLP_UNDEFINED;