tools: PCI: Fix broken pcitest compilation

pcitest is currently broken due to the following compiler error
and related warning. Fix by changing the run_test() function
signature to return an integer result.

pcitest.c: In function run_test:
pcitest.c:143:9: warning: return with a value, in function
returning void
  return (ret < 0) ? ret : 1 - ret; /* return 0 if test succeeded */

pcitest.c: In function main:
pcitest.c:232:9: error: void value not ignored as it ought to be
  return run_test(test);

Fixes: fef31eca ("tools: PCI: Fix compilation warnings")
Signed-off-by: Alan Mikhak <alan.mikhak@sifive.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Paul Walmsley <paul.walmsley@sifive.com>

tools/pci/pcitest.c

@@ -47,15 +47,15 @@ struct pci_test {
 	unsigned long	size;
 };
 
-static void run_test(struct pci_test *test)
+static int run_test(struct pci_test *test)
 {
-	long ret;
+	int ret = -EINVAL;
 	int fd;
 
 	fd = open(test->device, O_RDWR);
 	if (fd < 0) {
 		perror("can't open PCI Endpoint Test device");
-		return;
+		return -ENODEV;
 	}
 
 	if (test->barnum >= 0 && test->barnum <= 5) {