ext4: remove set but not used variable 'es'

Fix the following gcc warning:

fs/ext4/super.c:599:27: 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/20200402033939.25303-1-yanaijie@huawei.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/super.c

@@ -596,7 +596,6 @@ void __ext4_error_file(struct file *file, const char *function,
 {
 	va_list args;
 	struct va_format vaf;
-	struct ext4_super_block *es;
 	struct inode *inode = file_inode(file);
 	char pathname[80], *path;
 
@@ -604,7 +603,6 @@ void __ext4_error_file(struct file *file, const char *function,
 		return;
 
 	trace_ext4_error(inode->i_sb, function, line);
-	es = EXT4_SB(inode->i_sb)->s_es;
 	if (ext4_error_ratelimit(inode->i_sb)) {
 		path = file_path(file, pathname, sizeof(pathname));
 		if (IS_ERR(path))