fastboot: turn on -Werror

- Deal with a missing initializer issue
- Deal with some -Wunused issues
- Deal with some signed/unsigned issues
- switch to usleep from sleep to facilitate win_sdk compile

Change-Id: I64e32a5b0782aeed9582f489e866173c4df1afbf
diff --git a/fastboot/usb_windows.c b/fastboot/usb_windows.c
index f666015..0d13863 100644
--- a/fastboot/usb_windows.c
+++ b/fastboot/usb_windows.c
@@ -178,7 +178,7 @@
 
             count += written;
             len -= written;
-            data += written;
+            data = (const char *)data + written;
 
             if (len == 0)
                 return count;