MAINTAINERS: Add Manivannan Sadhasivam as the Reviewer for Generic PHY Framework

I'm volunteering to review the PHY patches. Hence, add myself as the
Reviewer.

Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20260811143417.336664-1-mani@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>