ntfs: decompress: remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], this
moves the stack buffer used during decompression to be allocated
externally.

The existing "dest_max_index" used in the VLA is bounded by cb_max_page.
cb_max_page is bounded by max_page, and max_page is bounded by nr_pages.
Since nr_pages is used for the "pages" allocation, it can similarly be
used for the "completed_pages" allocation and passed into the
decompression function.  The error paths are updated to free the new
allocation.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Link: http://lkml.kernel.org/r/20180626172909.41453-3-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Anton Altaparmakov <anton@tuxera.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>