net: systemport: fix double shift of a vlan_tci by VLAN_PRIO_SHIFT

Currently the u16 skb->vlan_tci is being right  shifted twice by
VLAN_PRIO_SHIFT, once in the macro skb_vlan_tag_get_pri and explicitly
by VLAN_PRIO_SHIFT afterwards. The combined shift amount is larger than
the u16 so the end result is always zero.  Remove the second explicit
shift as this is extraneous.

Fixes: 6e9fdb60 ("net: systemport: Add support for VLAN transmit acceleration")
Addresses-Coverity: ("Operands don't affect result")
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>