file extent fix

file extent fix

I ran a test with latest fio using jobfile,

[global]
size=10m
[job1]
ioengine=sync
rw=write
filename=testfile

And second time,
[global]
size=30m --> size increased.
[job1]
ioengine=sync
rw=write
filename=testfile

fio did not extend the file to 30m.

In case of f->file_offset=0, f->io_size equals to f->real_file_size, hence no extend.
Following patch worked for me. But this patch will not handle the case where we have
to extend a file and with offset :(

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>