drivers/sbus/char/flash.c: flash_read should update ppos instead of file->f_pos

flash_read() updates file->f_pos directly instead of the ppos given.  The
VFS later updates the file->f_pos and overwrites it with the unchanged
value of ppos.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>