Ensure that .minfp and .maxfp are respected for FIO_OPT_FLOAT_LIST

option_init() overwrites the .minfp and .maxfp members defined in
fio_options[] which is wrong. Remove the code that overwrites these two
members and change the convention for no FIO_OPT_FLOAT_LIST limits from
(minfp == DBL_MIN && maxfp == DBL_MAX) into (minfp != 0 || maxfp != 0).

Fixes: 833491908a1a ("stats: Add a function to report completion latency percentiles")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>