RZ spectral: add default value of i_comp in scalar transforms (#1404)

Author: dpgrote

Source/FieldSolver/SpectralSolver/SpectralFieldDataRZ.H

@@ -45,11 +45,11 @@ class SpectralFieldDataRZ
         ~SpectralFieldDataRZ ();
 
         void ForwardTransform (const amrex::MultiFab& mf, const int field_index,
-                               const int i_comp);
+                               const int i_comp=0);
         void ForwardTransform (const amrex::MultiFab& mf_r, const int field_index_r,
                                const amrex::MultiFab& mf_t, const int field_index_t);
         void BackwardTransform (amrex::MultiFab& mf, const int field_index,
-                                const int i_comp);
+                                const int i_comp=0);
         void BackwardTransform (amrex::MultiFab& mf_r, const int field_index_r,
                                 amrex::MultiFab& mf_t, const int field_index_t);