MAINTAINERS: Add Zack as maintainer of vmmouse driver

Zack Rusin will be taking over the maintainership of the VMware
vmmouse driver. Update the MAINTAINERS file to reflect this change.

Signed-off-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Zack Rusin <zackr@vmware.com>
Link: https://lore.kernel.org/r/164574146977.654750.10918397477833459687.stgit@csail.mit.edu