fs/ocfs2/journal.h: add bits_wanted while calculating credits in ocfs2_calc_extend_credits

While adding extends to a file, the credits are calculated incorrectly
and if the requested clusters is more than one (or more because we used
a conservative limit) then we run out of journal credits and we hit an
assert in journalling code.

The function parameter bits_wanted variable was not used at all.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Jie Liu <jeff.liu@oracle.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>