xen/pciback: fix cast to restricted pci_ers_result_t and pci_power_t

This patch fix the following sparse warning by applying
__force cast to pci_ers_result_t and pci_power_t.

drivers/xen/xen-pciback/pci_stub.c:760:16: sparse: warning: cast to restricted pci_ers_result_t
drivers/xen/xen-pciback/conf_space_capability.c:125:22: sparse: warning: cast to restricted pci_power_t

No functional changes intended.

Signed-off-by: Min-Hua Chen <minhuadotchen@gmail.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Message-ID: <20240917233653.61630-1-minhuadotchen@gmail.com>
Signed-off-by: Juergen Gross <jgross@suse.com>