MAINTAINERS: Update Counter subsystem git tree repo link

The Counter subsystem git tree is now located on the kernel.org git
server.

Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Link: https://lore.kernel.org/r/075c91bb0af32d27a139112701b12b118a50edd6.1664318353.git.william.gray@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>