src/include: Add space after comma

Fix the following error detected by checkpatch.pl:

ERROR: space required after that ',' (ctx:VxV)

TEST=Build and run on Galileo Gen2

Change-Id: I297bfc3d03dc95b471d3bb4b13803e81963841b5
Signed-off-by: Lee Leahy <Leroy.P.Leahy@intel.com>
Reviewed-on: https://review.coreboot.org/18647
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/include/smp/atomic.h

@@ -29,7 +29,7 @@ typedef struct { int counter; } atomic_t;
  * Atomically sets the value of v to i.  Note that the guaranteed
  * useful range of an atomic_t is only 24 bits.
  */
-#define atomic_set(v,i)		(((v)->counter) = (i))
+#define atomic_set(v, i)	(((v)->counter) = (i))
 
 
 /**