Use () after function name

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

ChangeLog.d/error_const.txt

@@ -1,6 +1,6 @@
 Features
    * New functions in the error module return constant strings for
-     high- and low-level error codes, complementing mbedtls_strerror
+     high- and low-level error codes, complementing mbedtls_strerror()
      which constructs a string for any error code, including compound
      ones, but requires a writable buffer. Contributed by Gaurav Aggarwal
      in #3176.