net: dsa: b53: remove redundant premature assignment to new_pvid

Variable new_pvid is being assigned with a value that is never read,
the following if statement updates new_pvid with a new value in both
of the if paths. The assignment is redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>