drm/bridge: tc358768: remove unused variable

Remove the unused phy_delay_nsk variable, before it was wrongly used
to compute some register value, the fixed computation is no longer using
it and therefore can be removed.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230427142934.55435-10-francesco@dolcini.it