Make delay values unsigned

There is no reason for negative delays in our use cases:
 - We don't need it (to work around any quirks).
 - sleep() (POSIX) uses an unsigned argument.
 - usleep() (POSIX) uses an unsigned argument.
 - Sleep() (Windows) uses an unsigned argument.

Change all callees as well (without any complications).

Corresponding to flashrom svn r1782.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
diff --git a/flashrom.c b/flashrom.c
index 092572e..23728f6 100644
--- a/flashrom.c
+++ b/flashrom.c
@@ -485,7 +485,7 @@
 	flash->pgm->par.chip_readn(flash, buf, addr, len);
 }
 
-void programmer_delay(int usecs)
+void programmer_delay(unsigned int usecs)
 {
 	if (usecs > 0)
 		programmer_table[programmer].delay(usecs);