vconsole-setup: use a consistent log level when setfont fails with EX_OSERR

vconsole-setup: use a consistent log level when setfont fails with EX_OSERR

Since we accept that setfont(8) can fail with EX_OSERR and we dont treat it as
an error, dont log this failure at LOG_ERR.

Before:
-------
/usr/bin/setfont failed with exit status 71.           [LOG_ERR]
Setting fonts failed with a "system error", ignoring.  [LOG_NOTICE]

After:
-----
/usr/bin/setfont failed with a "system error" (EX_OSERR), ignoring.   [LOG_NOTICE]
Setting source virtual console failed, ignoring remaining ones        [LOG_NOTICE]

Follow-up for 93c9a9d235e2304500c490b4868534385f925c76