SecurityPkg: Fix spelling errors

https://bugzilla.tianocore.org/show_bug.cgi?id=2265

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Chao Zhang <chao.b.zhang@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>

SecurityPkg/RandomNumberGenerator/RngDxe/RdRand.c

@@ -79,7 +79,7 @@ RdRandGetSeed128 (
   UINT32      Index2;
 
   //
-  // Chose an arbitary key and zero the feed_forward_value (FFV)
+  // Chose an arbitrary key and zero the feed_forward_value (FFV)
   //
   for (Index = 0; Index < 16; Index++) {
     Key[Index] = (UINT8) Index;