Fix grayscale dds loading

(cherry picked from commit cbbcaa31d578085eba5c5f44eda6f35d8f1f54a6)

modules/dds/texture_loader_dds.cpp

@@ -61,7 +61,6 @@ enum DDSFormat {
 	DDS_BGR5A1,
 	DDS_BGR565,
 	DDS_BGR10A2,
-	DDS_INDEXED,
 	DDS_LUMINANCE,
 	DDS_LUMINANCE_ALPHA,
 	DDS_MAX
@@ -196,9 +195,9 @@ Ref<Resource> ResourceFormatDDS::load(const String &p_path, const String &p_orig
 		dds_format = DDS_BGR10A2;
 	} else if (format_flags & DDPF_RGB && !(format_flags & DDPF_ALPHAPIXELS) && format_rgb_bits == 16 && format_red_mask == 0x0000f800 && format_green_mask == 0x000007e0 && format_blue_mask == 0x0000001f) {
 		dds_format = DDS_BGR565;
-	} else if (!(format_flags & DDPF_ALPHAPIXELS) && format_rgb_bits == 8 && format_red_mask == 0xff && format_green_mask == 0xff && format_blue_mask == 0xff) {
+	} else if (!(format_flags & DDPF_ALPHAPIXELS) && format_rgb_bits == 8 && format_red_mask == 0xff) {
 		dds_format = DDS_LUMINANCE;
-	} else if ((format_flags & DDPF_ALPHAPIXELS) && format_rgb_bits == 16 && format_red_mask == 0xff && format_green_mask == 0xff && format_blue_mask == 0xff && format_alpha_mask == 0xff00) {
+	} else if ((format_flags & DDPF_ALPHAPIXELS) && format_rgb_bits == 16 && format_red_mask == 0xff && format_alpha_mask == 0xff00) {
 		dds_format = DDS_LUMINANCE_ALPHA;
 	} else if (format_flags & DDPF_INDEXED && format_rgb_bits == 8) {
 		dds_format = DDS_BGR565;