ext4: cleanup variable name in ext4_fc_del()

The variables "&EXT4_SB(inode->i_sb)->s_fc_lock" and "&sbi->s_fc_lock"
are the same lock.  This function uses a mix of both, which is a bit
unsightly and confuses Smatch.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/96008557-8ff4-44cc-b5e3-ce242212f1a3@stanley.mountain
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: Dan Carpenter

fs/ext4/fast_commit.c

@@ -291,9 +291,9 @@ void ext4_fc_del(struct inode *inode)
 		return;
 
 restart:
-	spin_lock(&EXT4_SB(inode->i_sb)->s_fc_lock);
+	spin_lock(&sbi->s_fc_lock);
 	if (list_empty(&ei->i_fc_list) && list_empty(&ei->i_fc_dilist)) {
-		spin_unlock(&EXT4_SB(inode->i_sb)->s_fc_lock);
+		spin_unlock(&sbi->s_fc_lock);
 		return;
 	}