include: Fix spelling

Change-Id: Iadc813bc8208278996b2b1aa20cfb156ec06fac9
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: http://review.coreboot.org/3755
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/include/console/console.h

@@ -60,7 +60,7 @@ extern struct console_driver econsole_drivers[];
 extern int console_loglevel;
 #else
 /* __PRE_RAM__ */
-/* Using a global varible can cause problems when we reset the stack
+/* Using a global variable can cause problems when we reset the stack
  * from cache as ram to ram. If we make this a define USE_SHARED_STACK
  * we could use the same code on all architectures.
  */