prereq: SetupHostCommand: fix wrong check result

prereq: SetupHostCommand: fix wrong check result

Tony has reported, that CI tools job is failing for him in macOS
container due to prereq check failure for GNU `install` utility.

Michael diagnosed it and from his traces it was clear, that the issue is
caused by a wrong return value in the success check case, so lets fix it
accordingly.

Fixes: f75204036ccc ("prereq-build: allow host command symlinks to update")
Reported-by: Tony Ambardar <[email protected]>
Diagnosed-by: Michael Pratt <[email protected]>
Signed-off-by: Petr Štetiar <[email protected]>