KVM: PPC: Book3S HV nestedv2: Fix an error handling path in gs_msg_ops_kvmhv_nestedv2_config_fill_info()

The return value of kvmppc_gse_put_buff_info() is not assigned to 'rc' and
'rc' is uninitialized at this point.
So the error handling can not work.

Assign the expected value to 'rc' to fix the issue.

Fixes: 19d31c5f ("KVM: PPC: Add support for nestedv2 guests")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/a7ed4cc12e0a0bbd97fac44fe6c222d1c393ec95.1706441651.git.christophe.jaillet@wanadoo.fr