ext3_mark_inode_dirty() (and several other callers) use the
ext3_reserve_inode_write() and ext3_mark_ioc_dirty() pair for journalling an
inode's backing block.

Because ext3_reserve_inode_write() gets journalling access to the block there
is no need for ext3_mark_iloc_dirty() to do it as well.

This change reduces the overhead of a write() from 2.7 microseconds to 1.95
on a 2.7G P4.