fs/super.c: use && instead of & for warn_on condition

This fixes the following sparse warning:

  fs/super.c:1202:9: warning: dubious: x & !y

Bitwise and logical and are equivalent here, but logical was intended.
The generated code is identical, with and without CONFIG_LOCKDEP.
Signed-off-by: Vincent Stehlé <vincent.stehle@freescale.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

fs/super.c

@@ -1199,7 +1199,7 @@ int __sb_start_write(struct super_block *sb, int level, bool wait)
 	else
 		ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
 
-	WARN_ON(force_trylock & !ret);
+	WARN_ON(force_trylock && !ret);
 	return ret;
 }
 EXPORT_SYMBOL(__sb_start_write);