configs/hifive_unleashed: add missing uboot custom hash file
Commit [1] enabled BR2_DOWNLOAD_FORCE_CHECK_HASHES for
hifive_unleashed_defconfig and added custom hash files. But it forgot
to add the custom hash for uboot. It was not detected at that time
because the U-Boot version was the same as the default "latest"
version and was providing its hash.
This defconfig fails to build since the default "latest" was bumped
in commit [2].
This commit fixes the issue by adding the missing uboot hash.
Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/9677167050
[1] https://gitlab.com/buildroot.org/buildroot/-/commit/1ba1055d3da2d98874aae1eedf1983a2ed933605
[2] https://gitlab.com/buildroot.org/buildroot/-/commit/c14ce5346d969e660cc788f2f4d8619b27c805a2
Signed-off-by: Julien Olivain <ju.o@free.fr>