KVM: x86: use timespec64 for KVM_HC_CLOCK_PAIRING

The hypercall was added using a struct timespec based implementation,
but we should not use timespec in new code.

This changes it to timespec64. There is no functional change
here since the implementation is only used in 64-bit kernels
that use the same definition for timespec and timespec64.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>