gitignore: simplify .gitignore file with pattern "/barebox*"
There is no source file prefixed "barebox" at the top directory.
Generated files there can be simply ignored with "/barebox*" pattern.
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>