rules: fix COMMITCOUNT logic

rules: fix COMMITCOUNT logic

The newly added $(COMMITCOUNT) variable was wrongly increased by plus
one. The addition should have been only added to $(AUTORELEASE) as
OpenWrt traditionally starts counting at one rather than zero.

$(AUTORELEASE) counts the commits since the last bump, which is zero on
the version bump commit itself.

This commit increases $(AUTORELEASE) by one while leaving $(COMMITCOUNT)
as is.

The base-files package is the only package using $(COMMITCOUNT) so far
and requires a pseudo commit to keep the PKG_RELEASE correct. A non
functional change (Copyright bump) is done in the next commit.

Signed-off-by: Paul Spooren <mail@aparcar.org>