tcg: Fix spelling in comment (varables -> variables)

Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

tcg/tcg.h

@@ -175,7 +175,7 @@ typedef enum TCGType {
 
 typedef tcg_target_ulong TCGArg;
 
-/* Define a type and accessor macros for varables.  Using a struct is
+/* Define a type and accessor macros for variables.  Using a struct is
    nice because it gives some level of type safely.  Ideally the compiler
    be able to see through all this.  However in practice this is not true,
    expecially on targets with braindamaged ABIs (e.g. i386).