net: dsa: hellcreek: Add missing TAPRIO dependency

Add missing dependency to TAPRIO to avoid build failures such as:

|ERROR: modpost: "taprio_offload_get" [drivers/net/dsa/hirschmann/hellcreek_sw.ko] undefined!
|ERROR: modpost: "taprio_offload_free" [drivers/net/dsa/hirschmann/hellcreek_sw.ko] undefined!

Fixes: 24dfc6eb ("net: dsa: hellcreek: Add TAPRIO offloading support")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Link: https://lore.kernel.org/r/20210128163338.22665-1-kurt@linutronix.de


Signed-off-by: Jakub Kicinski <kuba@kernel.org>