Fix |sscanf| format string in cpu-intel.c.

Fix the signness of the format flag in the |sscanf| call in cpu-intel.c.

Change-Id: I31251d79aa146bf9c78be47020ee83d30864a3d2
Reviewed-on: https://boringssl-review.googlesource.com/6921
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/crypto/cpu-intel.c b/crypto/cpu-intel.c
index 924bab0..6614f63 100644
--- a/crypto/cpu-intel.c
+++ b/crypto/cpu-intel.c
@@ -127,7 +127,7 @@
   const int invert = in[0] == '~';
   uint64_t v;
 
-  if (!sscanf(in + invert, "%" PRIi64, &v)) {
+  if (!sscanf(in + invert, "%" PRIu64, &v)) {
     return;
   }