UBIFS: make the dbg_lock spinlock static

Remove the usage of the 'dbg_lock' spinlock from 'dbg_err()' and make
it static.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
diff --git a/fs/ubifs/debug.c b/fs/ubifs/debug.c
index 3050628..1934084 100644
--- a/fs/ubifs/debug.c
+++ b/fs/ubifs/debug.c
@@ -36,7 +36,7 @@
 
 #ifdef CONFIG_UBIFS_FS_DEBUG
 
-DEFINE_SPINLOCK(dbg_lock);
+static DEFINE_SPINLOCK(dbg_lock);
 
 static const char *get_key_fmt(int fmt)
 {