cache invalidation error for buffered write

cache invalidation error for buffered write

The bug causes corruptions of data read from flash.

The original code performs cache invalidation from "adr" to "adr + len"
in do_write_buffer().  Since len and adr could be updated in the code
before invalidation - it causes improper setting of cache invalidation
regions.

Signed-off-by: Massimo Cirillo <maxcir@gmail.com>
Signed-off-by: Giuseppe D'Eliseo <giuseppedeliseo@gmail.com>
Acked-by: Nicolas Pitre <nico@cam.org>
Acked-by: Jörn Engel <joern@logfs.org>
Signed-off-by: David Woohouse <dwmw2@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>