Fix potential leak in fill_interpolants()

Fix found thanks to AddressSanitizer & piglit
glsl-1.50/execution/built-in-functions/gs-pow-vec3-vec3.shader_test.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

src/vrend_shader.c

@@ -2258,6 +2258,7 @@ static boolean fill_interpolants(struct dump_ctx *ctx, struct vrend_shader_info
    if (ctx->prog_type == TGSI_PROCESSOR_VERTEX || ctx->prog_type == TGSI_PROCESSOR_GEOMETRY)
       return TRUE;
 
+   free(sinfo->interpinfo);
    sinfo->interpinfo = calloc(ctx->num_interps, sizeof(struct vrend_interp_info));
    if (!sinfo->interpinfo)
       return FALSE;