mm: remove re-walk from mmap_region()

Using vma_iter_set() will reset the tree and cause a re-walk.  Use
vmi_iter_config() to set the write to a sub-set of the range.  Change
the file case to also use vmi_iter_config() so that the end is correctly
set.

Link: https://lkml.kernel.org/r/20230724183157.3939892-7-Liam.Howlett@oracle.com


Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>