vfio-pci/zdev: fix possible segmentation fault issue

stable inclusion
from stable-5.10.20
commit 9eb145398e6fd31f1224a70a69db5ee0882210ec
bugzilla: 50608

--------------------------------

[ Upstream commit 7e31d6dc ]

In case allocation fails, we must behave correctly and exit with error.

Fixes: e6b817d4 ("vfio-pci/zdev: Add zPCI capabilities to VFIO_DEVICE_GET_INFO")
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>