OvmfPkg/PciHotPlugInitDxe: clean up protocol usage comment

OvmfPkg/PciHotPlugInitDxe: clean up protocol usage comment

The driver always produces an instance of the
EFI_PCI_HOT_PLUG_INIT_PROTOCOL. The "SOMETIMES_PRODUCES" remark is an
oversight from the original v1->v2 patch update; v2 should have stated
"ALWAYS_PRODUCES":

http://mid.mail-archive.com/1468242274-12686-5-git-send-email-lersek@redhat.com

> Notes:
>     v2:
>     - drop the PcdPciBusHotplugDeviceSupport check, and the PcdLib
>       dependency with it [Jordan]

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Fixes: 8aba40b79267df761bd24d6874ae87f47a7bd3de
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>