Fix bsrange read,write value option pairs

Fix bsrange read,write value option pairs

The 'bs' and 'bssplit' configuration variables accept separate numbers
for read and write operations if you separate them with a comma. For
example: bssplit=1k/39:8k/50:64k/11,1k/29:8k/50:64k/21

The documentation for 'bsrange' says it works the same way, but if I try
to specify two ranges with a comma, I get an error when I run the app.
E.g. if I put this line in the configuration file: bsrange=1k-16k,2k-32k

I get this error output:

fio: pid=26861, err=22/file:engines/sync.c:62, func=xfer, error=Invalid argument

This patch fixes it.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>