curl: Mark curl_easy_setopt() results non-interesting

We don't care about them (and I don't know if we need to) so help
tooling (e.g. Coverity Scan CID #359813) by making this decision
explicit.

Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Change-Id: I8b192778ec73bf001c2e88a97065b5bbc25dd619
Reviewed-on: https://review.coreboot.org/c/em100/+/58425
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>