settings: Fix missing kernel.h include

Apparently, settings were relying on other headers
including kernel.h, once that include got removed from the
logger header samples fail to compile.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
diff --git a/subsys/settings/src/settings.c b/subsys/settings/src/settings.c
index 0e86ec7..998e4b9 100644
--- a/subsys/settings/src/settings.c
+++ b/subsys/settings/src/settings.c
@@ -9,6 +9,7 @@
 #include <stdio.h>
 #include <stdbool.h>
 #include <errno.h>
+#include <kernel.h>
 
 #include "settings/settings.h"
 #include "settings_priv.h"
diff --git a/subsys/settings/src/settings_store.c b/subsys/settings/src/settings_store.c
index 5e8d01c..3ee570b 100644
--- a/subsys/settings/src/settings_store.c
+++ b/subsys/settings/src/settings_store.c
@@ -12,6 +12,7 @@
 #include <stddef.h>
 #include <sys/types.h>
 #include <errno.h>
+#include <kernel.h>
 
 #include "settings/settings.h"
 #include "settings_priv.h"