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/flash.h b/flash.h
index e320ced..bfb0a49 100644
--- a/flash.h
+++ b/flash.h
@@ -56,7 +56,7 @@
 int register_shutdown(int (*function) (void *data), void *data);
 void *programmer_map_flash_region(const char *descr, uintptr_t phys_addr, size_t len);
 void programmer_unmap_flash_region(void *virt_addr, size_t len);
-void programmer_delay(int usecs);
+void programmer_delay(unsigned int usecs);
 
 #define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))