cpu/x86: 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: I97bbe8ba19680bdb99fa38daa5e18b440c338576
Signed-off-by: Lee Leahy <Leroy.P.Leahy@intel.com>
Reviewed-on: https://review.coreboot.org/18843
Tested-by: build bot (Jenkins)
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>
Reviewed-by: Martin Roth <martinroth@google.com>

src/cpu/x86/tsc/delay_tsc.c

@@ -116,7 +116,7 @@ static inline unsigned long get_clocks_per_usec(void)
 	return car_get_var(clocks_per_usec);
 }
 
-void udelay(unsigned us)
+void udelay(unsigned int us)
 {
 	unsigned long long start;
 	unsigned long long current;