hw/timer/mc146818rtc: White space clean-up

mc146818rtc.c still contains some TABs. Replace them with spaces.
And while we're at it, also delete trailing whitespace in this file.

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1534419358-10932-4-git-send-email-thuth@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>