arm: Move a png_debug statement to its correct place

It should be placed immediately after all variable declarations.

arm/palette_neon_intrinsics.c

@@ -30,8 +30,6 @@ png_riffle_palette_neon(png_structrp png_ptr)
    int num_trans = png_ptr->num_trans;
    int i;
 
-   png_debug(1, "in png_riffle_palette_neon");
-
    /* Initially black, opaque. */
    uint8x16x4_t w = {{
       vdupq_n_u8(0x00),
@@ -40,6 +38,8 @@ png_riffle_palette_neon(png_structrp png_ptr)
       vdupq_n_u8(0xff),
    }};
 
+   png_debug(1, "in png_riffle_palette_neon");
+
    /* First, riffle the RGB colours into an RGBA8 palette.
     * The alpha component is set to opaque for now.
     */