CVE-2023-52902 nommu: fix memory leak in do_mmap() error path

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

nommu: fix memory leak in do_mmap() error path

The preallocation of the maple tree nodes may leak if the error path to
“error_just_free” is taken. Fix this by moving the freeing of the maple
tree nodes to a shared location for all error paths.