Comment typo fix in mbedtls_pk_can_do_ext()

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/library/pk.c b/library/pk.c
index 4273d93..f25266a 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -295,7 +295,7 @@
                             PSA_KEY_USAGE_DECRYPT;
                 break;
             default:
-                /* Should never happend */
+                /* Should never happen */
                 return( 0 );
         }