ext4: remove set but not used variable 'es' in ext4_jbd2.c

Fix the following gcc warning:

fs/ext4/ext4_jbd2.c:341:30: warning: variable 'es' set but not used [-Wunused-but-set-variable]
     struct ext4_super_block *es;
                              ^~

Fixes: 2ea2fc775321 ("ext4: save all error info in save_error_info() and drop ext4_set_errno()")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200402034759.29957-1-yanaijie@huawei.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4_jbd2.c

@@ -338,9 +338,6 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,
 		if (inode && inode_needs_sync(inode)) {
 			sync_dirty_buffer(bh);
 			if (buffer_req(bh) && !buffer_uptodate(bh)) {
-				struct ext4_super_block *es;
-
-				es = EXT4_SB(inode->i_sb)->s_es;
 				ext4_error_inode_err(inode, where, line,
 						     bh->b_blocknr, EIO,
 					"IO error syncing itable block");