wined3d: fix a compiler warning

[Austin English]

Okay'ed by Henri

-- 
-Austin
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diff --git a/dlls/wined3d/arb_program_shader.c b/dlls/wined3d/arb_program_shader.c
index 44b4fce..f759372 100644
--- a/dlls/wined3d/arb_program_shader.c
+++ b/dlls/wined3d/arb_program_shader.c
@@ -922,11 +922,11 @@ static void shader_arb_get_register_name(const struct wined3d_shader_instruction
             {
                 if(This->baseShader.reg_maps.shader_version.major < 3)
                 {
-                    sprintf(register_name, ctx->texcrd_output[reg->idx]);
+                    sprintf(register_name, "%s", ctx->texcrd_output[reg->idx]);
                 }
                 else
                 {
-                    sprintf(register_name, ctx->vs_output[reg->idx]);
+                    sprintf(register_name, "%s", ctx->vs_output[reg->idx]);
                 }
             }
             break;