xfs: use correct log reservation when handling ENOSPC in xfs_create

We added the ENOSPC handling patch in xfs_create just after it got mered
with xfs_mkdir.  Change the log reservation to the variable for either
the create or mkdir value so it does the right thing if get here for creating
a directory.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>