debuginfod-find: Be a bit less verbose with -v

debuginfod-find: Be a bit less verbose with -v

debuginfod-find -v enables a progressfn that prints the Progress every
time the callback is called. For slow transfers or big downloads this
can be really verbose (hundreds a times a second). Slow it down a bit,
so it only prints the progress at most 5 times a second.

Signed-off-by: Mark Wielaard <mark@klomp.org>