xmb: fix confirm dialog Back/OK icons drawn at scale_factor squared

icon_size already bakes in last_scale_factor (50 * scale_factor), but
scale_factor was also passed as the xmb_draw_icon scale argument, which
re-applies it through the transform matrix. Effective icon size was
50 * scale_factor^2 instead of 50 * scale_factor, so the dpad/face-button
glyphs blew up and distorted at high resolution (correct at 1080p where
scale_factor is ~1.0, garbled at 4K where it is ~2.0). Pass 1 to match
every other xmb_draw_icon call site, which supply a pre-scaled size.

Author: LibretroAdmin

menu/drivers/xmb.c

@@ -1362,7 +1362,7 @@ static void xmb_render_messagebox_internal(
             video_height,
             xmb->alpha,
             0,
-            scale_factor,
+            1,
             col,
             xmb->shadow_offset / 2,
             mymat);
@@ -1435,7 +1435,7 @@ static void xmb_render_messagebox_internal(
             video_height,
             xmb->alpha,
             0,
-            scale_factor,
+            1,
             col,
             xmb->shadow_offset / 2,
             mymat);