mesa: Fix array out-of-bounds access by _mesa_TexGend.

_mesa_TexGend calls _mesa_TexGenfv, which uses the params argument
as an array.
diff --git a/src/mesa/main/texgen.c b/src/mesa/main/texgen.c
index d3ea7b9..f9d3821 100644
--- a/src/mesa/main/texgen.c
+++ b/src/mesa/main/texgen.c
@@ -181,8 +181,10 @@
 void GLAPIENTRY
 _mesa_TexGend(GLenum coord, GLenum pname, GLdouble param )
 {
-   GLfloat p = (GLfloat) param;
-   _mesa_TexGenfv( coord, pname, &p );
+   GLfloat p[4];
+   p[0] = (GLfloat) param;
+   p[1] = p[2] = p[3] = 0.0F;
+   _mesa_TexGenfv( coord, pname, p );
 }