generic/204: use more space for inode allocation

generic/204: use more space for inode allocation

On v4/512b and v5/1k xfs, there're not enough free inodes for new files
and generic/204 fails because of running out of inode not space.

Adding "-i maxpct=50" to MKFS_OPTIONS to bump up the inode limit at mkfs
time, and test could pass on all configurations.

Suggested-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>