m25p80: do not put iovec on the stack

m25p80: do not put iovec on the stack

When doing a read-modify-write cycle, QEMU uses the iovec after returning
from blk_aio_pwritev.  m25p80 puts the iovec on the stack of blk_aio_pwritev's
caller, which causes trouble in this case.  This has been a problem
since commit 243e6f6 ("m25p80: Switch to byte-based block access",
2016-05-12) started doing writes at a smaller granularity than 512 bytes.
In principle however it could have broken before when using -drive
if=mtd,cache=none on a disk with 4K native sectors.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-id: 1467138270-32481-3-git-send-email-clg@kaod.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>