BUG/MINOR: cfgparse: report proper location for log-format-sd errors

BUG/MINOR: cfgparse: report proper location for log-format-sd errors

When a parsing error occurs inside a log-format-sd expression, we report
the location of the log-format directive (which may not be set) instead
of reporting the proper log-format-sd directive location where the parsing
error occured.

 1|listen test
 2|  log-format "%B"      # no error
 3|  log-format-sd "%bad" # error

 | [ALERT]    (322261) : config : Parsing [empty.conf:2]: failed to parse log-format-sd : no such format variable 'bad'. If you wanted to emit the '%' character verbatim, you need to use '%%'.

The fix consists in using the config hints dedicated to log-format-sd
directive instead of the log-format one.

The bug was introduced in 8a4e4420 ("MEDIUM: log-format: Use standard
HAProxy log system to report errors").

This should be backported to every stable versions.