mm/mmu_notifier: clean up mmu_notifier.h kernel-doc

mm/mmu_notifier: clean up mmu_notifier.h kernel-doc

Eliminate kernel-doc warnings in mmu_notifier.h:
- add a missing struct short description
- use the correct format for function parameters
- add missing function return comment sections

Warning: include/linux/mmu_notifier.h:236 missing initial short
 description on line: * struct mmu_interval_notifier_ops
Warning: include/linux/mmu_notifier.h:325 function parameter 'interval_sub'
 not described in 'mmu_interval_set_seq'
Warning: include/linux/mmu_notifier.h:325 function parameter 'cur_seq'
 not described in 'mmu_interval_set_seq'
Warning: include/linux/mmu_notifier.h:346 function parameter 'interval_sub'
 not described in 'mmu_interval_read_retry'
Warning: include/linux/mmu_notifier.h:346 function parameter 'seq' not
 described in 'mmu_interval_read_retry'
Warning: include/linux/mmu_notifier.h:346 No description found for return
 value of 'mmu_interval_read_retry'
Warning: include/linux/mmu_notifier.h:370 function parameter 'interval_sub'
 not described in 'mmu_interval_check_retry'
Warning: include/linux/mmu_notifier.h:370 function parameter 'seq' not
 described in 'mmu_interval_check_retry'
Warning: include/linux/mmu_notifier.h:370 No description found for return
 value of 'mmu_interval_check_retry'

Link: https://lkml.kernel.org/r/20260302005222.3470783-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>