[MTD] physmap: resume already suspended chips on failure to suspend

A nice side effect of this patch is that the return value of
physmap_flash_suspend in the error path is the value of the first failing
suspend callback and not the bitwise OR of all of them.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>