net: mvpp2: Fix DMA address mask size

PPv2 TX/RX descriptors uses 40bits DMA addresses, but 41 bits masks were
used (GENMASK_ULL(40, 0)).

This commit fixes that by using the correct mask.

Fixes: e7c5359f ("net: mvpp2: introduce PPv2.2 HW descriptors and adapt accessors")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>