mm: Fix __vma_adjust() writes for the maple tree

mm: Fix __vma_adjust() writes for the maple tree

Only write when necessary to the maple tree.  This should only occur
when the VMA changes.  In the __vma_adjust() case, it is either the vma
when it is expanded, the next vma when the boundary expands into 'vma',
writing the 'insert', or when vma expands/shrinks for shift_arg_pages().

The mas_preallocate() setup should track the intended write to ensure
the correct number of nodes are preallocated for the pending write.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>