Avoid zero size allocation in cache_k8_northbridges()

kmalloc for flush_words resulted in zero size allocation when no
k8_northbridges existed.  Short circuit the code path for this case.

Also remove uneeded zeroing of num_k8_northbridges just after checking if
it is zero.
Signed-off-by: Ben Collins <bcollins@ubuntu.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86_64/kernel/k8.c

@@ -39,10 +39,10 @@ int cache_k8_northbridges(void)
 {
 	int i;
 	struct pci_dev *dev;
+
 	if (num_k8_northbridges)
 		return 0;
 
-	num_k8_northbridges = 0;
 	dev = NULL;
 	while ((dev = next_k8_northbridge(dev)) != NULL)
 		num_k8_northbridges++;
@@ -52,6 +52,11 @@ int cache_k8_northbridges(void)
 	if (!k8_northbridges)
 		return -ENOMEM;
 
+	if (!num_k8_northbridges) {
+		k8_northbridges[0] = NULL;
+		return 0;
+	}
+
 	flush_words = kmalloc(num_k8_northbridges * sizeof(u32), GFP_KERNEL);
 	if (!flush_words) {
 		kfree(k8_northbridges);