ext4: check for shutdown and r/o file system in ext4_write_inode()

commit 18f2c4fcebf2582f96cbd5f2238f4f354a0e4847 upstream.

If the file system has been shut down or is read-only, then
ext4_write_inode() needs to bail out early.

Also use jbd2_complete_transaction() instead of ext4_force_commit() so
we only force a commit if it is needed.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>