scsi: MAINTAINERS: Make cxlflash obsolete

The cxlflash driver is no longer actively maintained and we intend to
remove it in a future kernel release. Change its status to obsolete.

While we're here, Matthew Ochs no longer works at IBM and is no longer in a
position to access cxlflash hardware, so remove him from the maintainers
list.

Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Link: https://lore.kernel.org/r/20240409031027.41587-1-ajd@linux.ibm.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>