lisa._kmod: Workaround broken atomic headers in IKHEADERS

FIX

Headers found at /sys/kheaders.tar.xz generated when CONFIG_IKHEADERS=y
contain a broken version of the include/linux/atomic/*. headers. They
embed a sha1sum of the file on their last line, but
kernel/gen_kheaders.sh strips some multiline comments from the file,
changing the SHA1.

Work around the issue by updating the SHA1 in the file.