ffmpeg_opt: fix max_error_rate help info display issue.

ffmpeg -h display "max_error_rate" option help information have
been cut off, the root cause is used a wrong initial order.
Signed-off-by: Jun Zhao <jun.zhao@intel.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

fftools/ffmpeg_opt.c

@@ -3457,7 +3457,7 @@ const OptionDef options[] = {
     { "debug_ts",       OPT_BOOL | OPT_EXPERT,                       { &debug_ts },
         "print timestamp debugging info" },
     { "max_error_rate",  HAS_ARG | OPT_FLOAT,                        { &max_error_rate },
-        "maximum error rate", "ratio of errors (0.0: no errors, 1.0: 100% errors) above which ffmpeg returns an error instead of success." },
+        "ratio of errors (0.0: no errors, 1.0: 100% errors) above which ffmpeg returns an error instead of success.", "maximum error rate" },
     { "discard",        OPT_STRING | HAS_ARG | OPT_SPEC |
                         OPT_INPUT,                                   { .off = OFFSET(discard) },
         "discard", "" },