ext4: fix error paths in swap_inode_boot_loader()

In swap_inode_boot_loader() we forgot to release ->i_mutex and resume
unlocked dio for inode and inode_bl if there is an error starting the
journal handle.  This commit fixes this issue.

Reported-by: Ahmed Tamrawi <ahmedtamrawi@gmail.com>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Dr. Tilmann Bubeck <t.bubeck@reinform.de>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org  # v3.10+