CVE-2026-98224: mm/vma: correctly unaccount on mmap_prepare() failure

In the Linux kernel, the following vulnerability has been resolved:

mm/vma: correctly unaccount on mmapprepare() failure

mmapsetup() accounts memory for relevant mappings via:

securityvmenoughmemorymm() -> vmenoughmemory() -> vmacctmemory()

If mmapsetup() fails, this indicates that this accounting did not take place, and thus it's appropriate for mmapregion() to jump to abortmunmap.

However if callmmapprepare() fails, it also jumps there and any accounted memory is not correctly unaccounted.

Fix this by handling each error separately.