arch: Kconfig: fix spelling mistake "seperate" -> "separate"

Threre is a spelling mistake in the Kconfig text. Fix it.

Link: https://lkml.kernel.org/r/20210704095207.37342-1-colin.king@canonical.comSigned-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/Kconfig

@@ -886,7 +886,7 @@ config HAVE_SOFTIRQ_ON_OWN_STACK
 	bool
 	help
 	  Architecture provides a function to run __do_softirq() on a
-	  seperate stack.
+	  separate stack.
 
 config PGTABLE_LEVELS
 	int