Revert "Unsignify lengths and addresses in chip functions and structs"

- probe_timing was changed to unsigned although we use negative values
  for special cases
- some code was not changed along hence did no longer compile:
  * dediprog's read and write functions
  * linux_spi's read and write functions
- it introduced a number of new sign conversion warnings
  (http://paste.flashrom.org/view.php?id=832)

To be safe this patch reverts all changes made in r1448, a corrected
patch will follow later.

Thanks to idwer for pointing out the problem first!

Corresponding to flashrom svn r1450.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
diff --git a/serprog.c b/serprog.c
index a4aef08..9d554c9 100644
--- a/serprog.c
+++ b/serprog.c
@@ -795,7 +795,7 @@
  * the advantage that it is much faster for most chips, but breaks those with
  * non-contiguous address space (like AT45DB161D). When spi_read_chunked is
  * fixed this method can be removed. */
-int serprog_spi_read(struct flashchip *flash, uint8_t *buf, unsigned int start, unsigned int len)
+int serprog_spi_read(struct flashchip *flash, uint8_t *buf, int start, int len)
 {
 	int i;
 	int cur_len;