Fix unpaired parentheses in a formatting string

  Fix unpaired parentheses in the format statement used in an error message
about OBC segment data not being on the supergrid.  All answers are bitwise
identical, but there is one less compile-time warning.

src/core/MOM_open_boundary.F90

@@ -854,7 +854,7 @@ subroutine initialize_segment_data(G, GV, US, OBC, PF)
 !       if (siz(4) == 1) segment%values_needed = .false.
         if (segment%on_pe) then
           if (OBC%brushcutter_mode .and. (modulo(siz(1),2) == 0 .or. modulo(siz(2),2) == 0)) then
-            write(mesg,'("Brushcutter mode sizes ", I6, I6))') siz(1), siz(2)
+            write(mesg,'("Brushcutter mode sizes ", I6, I6)') siz(1), siz(2)
             call MOM_error(WARNING, mesg // " " // trim(filename) // " " // trim(fieldname))
             call MOM_error(FATAL,'segment data are not on the supergrid')
           endif