MAINTAINERS: Update website and git repo for Wolfson Microelectronics

Support for Wolfson Microelectronics devices is now part of Cirrus Logic
and the relevant parts of the old opensource.wolfsonmicro.com site have
moved to the Cirrus Logic GitHub area.

This patch updates the website and git repo links, and also removes an
obsolete website link for the voltage and current drivers.

Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>