[XTENSA] Spelling fixes in arch/xtensa

Spelling fixes in arch/xtensa/.

Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
Signed-off-by: Chris Zankel <chris@zankel.net>
diff --git a/arch/xtensa/mm/init.c b/arch/xtensa/mm/init.c
index e1ec2d1..8415c76 100644
--- a/arch/xtensa/mm/init.c
+++ b/arch/xtensa/mm/init.c
@@ -205,7 +205,7 @@
 	/* Writing zeros to the <t>TLBCFG special registers ensure
 	 * that valid values exist in the register.  For existing
 	 * PGSZID<w> fields, zero selects the first element of the
-	 * page-size array.  For nonexistant PGSZID<w> fields, zero is
+	 * page-size array.  For nonexistent PGSZID<w> fields, zero is
 	 * the best value to write.  Also, when changing PGSZID<w>
 	 * fields, the corresponding TLB must be flushed.
 	 */