xHCI: Remove redundant variable in xhci_resume()

Set hcd->state = HC_STATE_SUSPENDED if there is a power loss during system
resume or the system is hibernated, otherwise leave it be. The variable
old_state is redundant and made an unreachable code path, so remove it.

Signed-off-by: Andiry Xu <andiry.xu@amd.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>