Follow-up to r1483575: Stylistic fix.

* subversion/include/svn_types.h
  (SVN_UNALIGNED_ACCESS_IS_OK): add parentheses around the things we test

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1483580 13f79535-47bb-0310-9956-ffa450edef68