quota: Use the pre-processor to compile out quotactl_cmd_write when !CONFIG_BLOCK

quotactl_cmd_write() is only ever invoked when BLOCK is configured. When
!CONFIG_BLOCK, the build warning below is displayed. Let's fix that.

fs/quota/quota.c:311:12: warning: ‘quotactl_cmd_write’ defined but not used [-Wunused-function]

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/quota/quota.c

@@ -307,6 +307,8 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
 	}
 }
 
+#ifdef CONFIG_BLOCK
+
 /* Return 1 if 'cmd' will block on frozen filesystem */
 static int quotactl_cmd_write(int cmd)
 {
@@ -322,6 +324,8 @@ static int quotactl_cmd_write(int cmd)
 	return 1;
 }
 
+#endif /* CONFIG_BLOCK */
+
 /*
  * look up a superblock on which quota ops will be performed
  * - use the name of a block device to find the superblock thereon