migration: replace assert(false) with g_assert_not_reached()

This patch is part of a series that moves towards a consistent use of
g_assert_not_reached() rather than an ad hoc mix of different
assertion mechanisms.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-ID: <20240919044641.386068-14-pierrick.bouvier@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>

migration/dirtyrate.c

@@ -228,7 +228,7 @@ static int time_unit_to_power(TimeUnit time_unit)
     case TIME_UNIT_MILLISECOND:
         return -3;
     default:
-        assert(false); /* unreachable */
+        g_assert_not_reached();
         return 0;
     }
 }