pstore: Remove unused vmalloc.h in pmsg

Since the vmalloc code has been removed from write_pmsg() in the commit
"5bf6d1b9 pstore/pmsg: drop bounce buffer", remove the unused header
vmalloc.h.
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/pmsg.c

@@ -15,7 +15,6 @@
 #include <linux/device.h>
 #include <linux/fs.h>
 #include <linux/uaccess.h>
-#include <linux/vmalloc.h>
 #include "internal.h"
 
 static DEFINE_MUTEX(pmsg_lock);