BUG/MINOR: mux-h2: Fix typo in scheme adjustment

BUG/MINOR: mux-h2: Fix typo in scheme adjustment

That comma should've been a semicolon. Fortunately, as it is now there
is no impact thanks to operators precedence, and all expressions are
properly evaluated. But this is troubling and the risk is high to
turn it into an effective bug with a minor change.

Introduced in b8ce8905cf63ecd06b36af39c05103fadf3cc347 which first
appeared in 2.1-dev3. This fix must be backported to 2.1+.

(cherry picked from commit a3298023b04923ba12429d79c559dc7a850ae122)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>