make it lower case

Author: Hyeoksu Lee

src/post_process/m_global_parameters.fpp

@@ -423,7 +423,7 @@ contains
             fluid_pp(i)%qv = 0._wp
             fluid_pp(i)%qvp = 0._wp
             fluid_pp(i)%G = dflt_real
-            fluid_pp(i)%D_v = dflt_Real
+            fluid_pp(i)%D_v = dflt_real
         end do
 
         ! Formatted database file(s) structure parameters