MAINTAINERS: add linux-next info

Add linux-next info to MAINTAINERS for ease of finding this data.

Link: https://lkml.kernel.org/r/20230704054410.12527-1-rdunlap@infradead.org


Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>