process.c: ix typo

* process.c (USE_GETPWNAM_R): fix typo.  _SC_GETPW_R_SIZE_MAX instead
  of same macro twice.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39146 b2dd03c8-39d4-4d8f-98ff-823fe69b080e