fix crash: free of wrong pointer in bssplit_ddir

fix crash: free of wrong pointer in bssplit_ddir

I got SIGABRT when I passed "bssplit=4k/10:64k/50:/40" to fio.
It should be "bssplit=4k/10:64k/50:32k/40" but I missed "32k" in
my typing. The bug turns out to be another typo just like mine:)

*** glibc detected *** /viki/lkml/fio/fio: free(): invalid pointer:
0x000000000071fd30 ***
======= Backtrace: =========
/lib/libc.so.6(+0x78bb6)[0x7ffff700cbb6]
/lib/libc.so.6(cfree+0x73)[0x7ffff7013483]
/viki/lkml/fio/fio[0x42c108]
/viki/lkml/fio/fio[0x42c475]
/viki/lkml/fio/fio[0x429194]
/viki/lkml/fio/fio[0x42a888]
/viki/lkml/fio/fio(parse_option+0x101)[0x42ac47]
/viki/lkml/fio/fio(fio_options_parse+0x95)[0x42e5b3]
/viki/lkml/fio/fio(parse_jobs_ini+0x3ae)[0x4103ae]
/viki/lkml/fio/fio(parse_options+0x112)[0x41198a]
/viki/lkml/fio/fio(main+0x3b)[0x460f5b]
/lib/libc.so.6(__libc_start_main+0xfd)[0x7ffff6fb2c4d]
/viki/lkml/fio/fio[0x40a7c9]

Signed-off-by: Hong Zhiguo <zhiguohong@tencent.com>
Tested-by: Hong Zhiguo <zhiguohong@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>