Fix typos in comments

Co-authored-by: Janos Follath <janos.follath@arm.com>
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 124c597..91d54ca 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1915,7 +1915,7 @@
  *
  * This setting requires compiling with clang -fsanitize=memory.
  *
- * Uncomment to enable testing of the constant-flow nature of seletected code.
+ * Uncomment to enable testing of the constant-flow nature of selected code.
  */
 //#define MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN