jbd2: fix /proc setup for devices that contain '/' in their names

trimed down version of commit 05496769e5da83ce22ed97345afd9c7b71d6bd24 upstream.

Some devices such as "cciss/c0d0p9" will cause jbd2 setup and teardown
failures when /proc filenames are created with embedded slashes.  This
is a slimmed down version of commit 05496769, with the stack reduction
aspects of the patch omitted to meet the -stable criteria.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>