Now that we use kzalloc() to allocate the hbus buffer, we must call
kfree() in the error path as well to prevent memory leakage.

Fixes: 877b911a ("PCI: hv: Avoid a kmemleak false positive caused by the hbus buffer")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>