MAINTAINERS: Add Maira to VKMS maintainers

I've been contributing to VKMS with improvements, reviews, testing and
debugging. Therefore, add myself as a co-maintainer of the VKMS driver.

Acked-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230508141038.327160-1-mairacanal@riseup.net