soc/intel/broadwell: Add int to unsigned

Fix the following issue detected by checkpatch:

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

TEST=None

Change-Id: Iae22e724b6adae16248db7dc8f822f65bfadae5f
Signed-off-by: Lee Leahy <Leroy.P.Leahy@intel.com>
Reviewed-on: https://review.coreboot.org/18873
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>

src/soc/intel/broadwell/igd.c

@@ -277,7 +277,7 @@ static inline void gtt_rmw(u32 reg, u32 andmask, u32 ormask)
 
 static int gtt_poll(u32 reg, u32 mask, u32 value)
 {
-	unsigned try = GT_RETRY;
+	unsigned int try = GT_RETRY;
 	u32 data;
 
 	while (try--) {