sm501: Fix hardware cursor color conversion

According to the sm501 specs the hardware cursor colors are to be given in
the rgb565 format, but the code currently interprets them as bgr565.

Therefore, the colors of the hardware cursors are wrong in the QEMU
display, e.g., the standard mouse pointer of AmigaOS appears blue instead
of red. This change fixes this issue by replacing the existing naive
bgr565 => rgb888 conversion with a standard rgb565 => rgb888 one that also
scales the color component values properly.

Signed-off-by: Sebastian Bauer <mail@sebastianbauer.info>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/display/sm501.c

@@ -652,9 +652,9 @@ static inline void get_hwc_palette(SM501State *state, int crt, uint8_t *palette)
         } else {
             rgb565 = color_reg & 0xFFFF;
         }
-        palette[i * 3 + 0] = (rgb565 << 3) & 0xf8; /* red */
-        palette[i * 3 + 1] = (rgb565 >> 3) & 0xfc; /* green */
-        palette[i * 3 + 2] = (rgb565 >> 8) & 0xf8; /* blue */
+        palette[i * 3 + 0] = ((rgb565 >> 11) * 527 + 23) >> 6; /* r */
+        palette[i * 3 + 1] = (((rgb565 >> 5) & 0x3f) * 259 + 33) >> 6; /* g */
+        palette[i * 3 + 2] = ((rgb565 & 0x1f) * 527 + 23) >> 6; /* b */
     }
 }