image.bbclass: do exact match for rootfs type
Do exact match for rootfs type, instead of pattern match, to avoid
unexpected build error due to redundant rootfs type build.
E.g. when building ext2.gz.u-boot, both .gz.u-boot and .u-boot are matched,
the following build error will appear, actually .u-boot is not needed.
| mkimage: Can't open .../core-image-minimal-<machine>-<yyyymmddhhmmss>.rootfs.ext2.gz: No such file or directory
(From OE-Core rev:
46bc438374de74af76d288520c6252c9b7840767)
Signed-off-by: Zhenhua Luo <zhenhua.luo@nxp.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
