net: dsa: mv88e6xxx: Fix off-by-one in VTU devlink region size

net: dsa: mv88e6xxx: Fix off-by-one in VTU devlink region size

[ Upstream commit 281140a0a2ce4febf2c0ce5d29d0e7d961a826b1 ]

In the unlikely event of the VTU being loaded to the brim with 4k
entries, the last one was placed in the buffer, but the size reported
to devlink was off-by-one. Make sure that the final entry is available
to the caller.

Fixes: ca4d632aef03 ("net: dsa: mv88e6xxx: Export VTU as devlink region")
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>