MAINTAINERS: Update VME subsystem tree.

VME Subsystem lists driver-core repository as canonical tree. Greg has
stated that char-misc should be used for submissions instead[1].

[1] https://lkml.org/lkml/2017/9/1/486



Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>