image.bbclass: Correct chaining compression support
When chaining of compression/conversion types was added, we had a new
way to handle doing things like "ext4.bz2.sha256sum" or
"ext2.gz.u-boot". However, because the U-Boot image class isn't
included normally, it wasn't properly converted at the time. After the
support was added the "clean" argument that the .u-boot code uses no
longer functions. The fix for this inadvertently broke chaining
compression/conversion. First, correct the u-boot conversion code.
Fixes: 46bc438374de ("image.bbclass: do exact match for rootfs type") Cc: Zhenhua Luo <zhenhua.luo@nxp.com> Cc: Richard Purdie <richard.purdie@linuxfoundation.org> Cc: Patrick Ohly <patrick.ohly@intel.com> Signed-off-by: Tom Rini <trini@konsulko.com> Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
