ext4: rename journal_dev to s_journal_dev inside ext4_sb_info

[ Upstream commit ee7ed3aa0f08621dbf897d2a98dc6f2c7e7d0335 ]

Rename journal_dev to s_journal_dev inside ext4_sb_info, keep
the naming rules consistent with other variables, which is
convenient for code reading and writing.

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/1600916623-544-1-git-send-email-brookxu@tencent.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Stable-dep-of: 26fb5290240d ("ext4: Fix reusing stale buffer heads from last failed mounting")
Signed-off-by: Sasha Levin <sashal@kernel.org>