hwtracing: stm: fix build error on some arches

Commit b5e2ced9 ("stm class: Use vmalloc for the master map") caused
a build error on some arches as vmalloc.h was not explicitly included.

Fix that by adding it to the list of includes.

Fixes: b5e2ced9 ("stm class: Use vmalloc for the master map")
Reported-by: Nkbuild test robot <lkp@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/stm/core.c

@@ -19,6 +19,7 @@
 #include <linux/stm.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/vmalloc.h>
 #include "stm.h"
 
 #include <uapi/linux/stm.h>