ext4: fix bigalloc regression

ext4: fix bigalloc regression

commit d0abafac8c9162f39c4f6b2f8141b772a09b3770 upstream.

Commit f5a44db5d2 introduced a regression on filesystems created with
the bigalloc feature (cluster size > blocksize).  It causes xfstests
generic/006 and /013 to fail with an unexpected JBD2 failure and
transaction abort that leaves the test file system in a read only state.
Other xfstests run on bigalloc file systems are likely to fail as well.

The cause is the accidental use of a cluster mask where a cluster
offset was needed in ext4_ext_map_blocks().

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>