stage6/04-gnuradio-m2k: switch libm2k to v0.8.0

There are some fixes that got into libm2k repo, so instead of updating
next_stable branch to latest main and keep using next_stable, just use
the release tag v0.8.0 which was also tested.

Signed-off-by: Stefan Raus <Stefan.Raus@analog.com>

stage6/04-gnuradio-m2k/00-run.sh

@@ -1,6 +1,6 @@
 #!/bin/bash -e
 
-LIBM2K_BRANCH="next_stable"
+LIBM2K_BRANCH="v0.8.0"
 GRIIO_BRANCH="upgrade-3.8" # let this to 'upgrade-3.8' since GNU Radio is 3.8.2
 GRM2K_BRANCH="maint-3.8" # let this to 'maint-3.8' since GNU Radio installed in Kuiper is 3.8.2
 LIBSIGROKDECODE_BRANCH="master"