Fix some errors scan-build found.
Fix some errors scan-build found.

This fixes a couple of failures to check for NULL in string parsing, and
one failure to free a value in an error path.

Signed-off-by: Peter Jones <2e0a021e603479ff81838c00c3b770daca4e0214@redhat.com>

rhinstaller/efivar,rhboot/efivar,rhboot/efivar,rhinstaller/efivar,vathpela/efivar-devel