lint: simplify board-status check

git can do lots of things by itself, no need to parse
its output and redo that.

Change-Id: Id2cdd2ea8d34c1ba2b0abddc88e1f3260d74f47d
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/6798
Tested-by: build bot (Jenkins)
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>