fix an incorrect typedef and cast

which was of no consequence,
  because nobody made use of it.

ancient, already in the very first commit of ngspice
  Date:   Thu Apr 27 20:03:57 2000 +0000

src/include/ngspice/smpdefs.h

@@ -2,7 +2,7 @@
 #define ngspice_SMPDEFS_H
 
 typedef  struct MatrixFrame     SMPmatrix;
-typedef  struct MatrixElement  *SMPelement;
+typedef  struct MatrixElement   SMPelement;
 
 /**********
 Copyright 1990 Regents of the University of California.  All rights reserved.

src/maths/sparse/spsmp.c

@@ -464,7 +464,7 @@ SMPfindElt(SMPmatrix *eMatrix, int Row, int Col, int CreateIfMissing)
     Col = Matrix->ExtToIntColMap[Col];
     Element = Matrix->FirstInCol[Col];
     Element = spcFindElementInCol(Matrix, &Element, Row, Col, CreateIfMissing);
-    return (SMPelement *)Element;
+    return Element;
 }
 
 /* XXX The following should probably be implemented in spUtils */