cpu/intel: Add int to unsigned

Fix the following warning detected by checkpatch.pl:

WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

TEST=Build and run on Galileo Gen2

Change-Id: I207713a3370e5a9abed4535187aa2aaeef502d6f
Signed-off-by: Lee Leahy <Leroy.P.Leahy@intel.com>
Reviewed-on: https://review.coreboot.org/18848
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/cpu/intel/hyperthreading/intel_sibling.c

@@ -53,7 +53,7 @@ int intel_ht_sibling(void)
 
 void intel_sibling_init(struct device *cpu)
 {
-	unsigned i, siblings;
+	unsigned int i, siblings;
 	struct cpuid_result result;
 
 	/* On the bootstrap processor see if I want sibling cpus enabled */