version: Change error to info for missing MANIFEST fields

The MANIFEST had an optional field Extended Version that was set to an
empty string by default. With the addition of the optional field
Compatible Names, the optional fields in the MANIFEST were removed
instead of being added as empty string as default:
https://gerrit.openbmc.org/c/openbmc/openbmc/+/52355

This causes an error message in the journal on every update:
phosphor-version-software-manager[528]: No values found in MANIFEST file for key: ExtendedVersion=
phosphor-version-software-manager[528]: No values found in MANIFEST file for key: CompatibleName=

Change the error message from severity error to info, so that the
message is still displayed, but it's not marked as an error.

Tested: The messages are not highlighted as errors in the journal.

Change-Id: I3c8c1d4f4767a12ab032bba0b4520add95f853b2
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/version.cpp b/version.cpp
index f7fbd2b..847148e 100644
--- a/version.cpp
+++ b/version.cpp
@@ -93,7 +93,7 @@
 
     if (values.empty())
     {
-        error("No values found in MANIFEST file for key: {KEY}", "KEY", key);
+        info("No values found in MANIFEST file for key: {KEY}", "KEY", key);
     }
 
     return values;