dfu-internal, dfu_host_ops: change prototype of start_file_rx() method.
dfu-internal, dfu_host_ops: change prototype of start_file_rx() method.

+ Method can fail.
+ Pass struct dfu_binary_file * directly, since it contains a
  struct dfu_host *

ciminaghi/libdfu,ciminaghi/libdfu,ciminaghi/libdfu