Description: vdpa: clean up get_config_size ret value handling
References:
 https://lore.kernel.org/netdev/20220123001216.2460383-13-sashal@kernel.org/
 https://bugzilla.redhat.com/show_bug.cgi?id=2057506
 https://www.openwall.com/lists/oss-security/2022/04/02/1
Notes:
 carnil> CONFIG_VHOST_VDPA not set in Debian.
 bwh> The vhost vDPA backend was introduced in 5.7.
 bwh> The change in 5.17 is described as only clean up, while the actual
 bwh> fix was commit 3ed21c1451a1, already included in all vulnerable
 bwh> branches.
Bugs:
upstream: released (5.16-rc6) [3ed21c1451a14d139e1ceb18f2fa70865ce3195a]
5.10-upstream-stable: released (5.10.88) [51f6302f81d243772047a74ffeceddfb11c964d5]
4.19-upstream-stable: N/A "Vulnerable code not present"
4.9-upstream-stable: N/A "Vulnerable code not present"
sid: released (5.15.15-1)
5.10-bullseye-security: released (5.10.92-1)
4.19-buster-security: N/A "Vulnerable code not present"
4.9-stretch-security: N/A "Vulnerable code not present"