x86: Fix misspellings in comments

Signed-off-by: Adam Buchbinder <adam.buchbinder@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: trivial@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/purgatory/stack.S

@@ -8,7 +8,7 @@
  */
 
 	/* A stack for the loaded kernel.
-	 * Seperate and in the data section so it can be prepopulated.
+	 * Separate and in the data section so it can be prepopulated.
 	 */
 	.data
 	.balign 4096