Get rid of sp_die()

- Add return values to sp_flush_stream(), sp_pass_writen(),
  sp_execute_opbuf(), sp_execute_opbuf_noflush(),
  sp_check_opbuf_usage(), sp_do_read_n().
- Use those return values to propagate errors instead of exiting.
  In some places this has to wait for core API changes (error handling for
  chip_readb, chip_readn, chip_write) hence comments are added instead.

Corresponding to flashrom svn r1719.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>

programmer.h

@@ -661,7 +661,6 @@ typedef int fdtype;
 void sp_flush_incoming(void);
 fdtype sp_openserport(char *dev, unsigned int baud);
 int serialport_config(fdtype fd, unsigned int baud);
-void __attribute__((noreturn)) sp_die(char *msg);
 extern fdtype sp_fd;
 /* expose serialport_shutdown as it's currently used by buspirate */
 int serialport_shutdown(void *data);