net: mvpp2: fix possible invalid pointer dereference

It will cause invalid pointer dereference to priv->cm3_base behind,
if PTR_ERR(priv->cm3_base) in mvpp2_get_sram().

Fixes: e54ad1e0 ("net: mvpp2: add CM3 SRAM memory map")
Signed-off-by: Hui Tang <tanghui20@huawei.com>
Link: https://lore.kernel.org/r/20221117084032.101144-1-tanghui20@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>