ptp: MAINTAINERS: drop Jeff Sipek

Emails to Jeff Sipek bounce:

  Your message to jsipek@vmware.com couldn't be delivered.
  Recipient is not authorized to accept external mail
  Status code: 550 5.7.1_ETR

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240327081413.306054-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>