Fix sp_openserport users on Windows

Corresponding to flashrom svn r1627.
Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Idwer Vollering <vidwer@gmail.com>

buspirate_spi.c

@@ -40,7 +40,7 @@ static int buspirate_serialport_setup(char *dev)
 {
 	/* 115200bps, 8 databits, no parity, 1 stopbit */
 	sp_fd = sp_openserport(dev, 115200);
- 	if (sp_fd < 0)
+ 	if (sp_fd == SER_INV_FD)
 		return 1;
 	return 0;
 }

pony_spi.c

@@ -116,7 +116,7 @@ int pony_spi_init(void)
 	arg = extract_programmer_param("dev");
 	if (arg && strlen(arg)) {
 		sp_fd = sp_openserport(arg, 9600);
-		if (sp_fd < 0) {
+		if (sp_fd == SER_INV_FD) {
 			free(arg);
 			return 1;
 		}

serprog.c

@@ -372,7 +372,7 @@ int serprog_init(void)
 		}
 		if (strlen(device)) {
 			sp_fd = sp_openserport(device, atoi(baudport));
-			if (sp_fd < 0) {
+			if (sp_fd == SER_INV_FD) {
 				free(device);
 				return 1;
 			}