Fix ETC quality setting

[madmiraal]

To compress VRAM textures takes time. b19225b ensured that ETC compression was as fast as possible. However, there were three issues with this change:

godot/modules/etc/image_compress_etc.cpp

Lines 167 to 175 in 545c894

	float effort = 0.0; //default, reasonable time
	if (p_lossy_quality > 0.75) {
	effort = 0.4;
	} else if (p_lossy_quality > 0.85) {
	effort = 0.6;
	} else if (p_lossy_quality > 0.95) {
	effort = 0.8;
	}

1. The else if statements will never be true so the higher settings will never be applied.
2. ETC effort is a value between 0 and 100, not 0 and 1; so even with 0.4 the effort value is effectively 0 (although there is still a difference, as ETC checks if the value is > 0).
3. There is an artificial shift between the lossy_quality setting and the effort applied.

This PR addresses the first two issues. I haven't addressed the third issue, because I suspect there was a reason for introducing this shift: most of the benefit from ETC compression is obtained between 40 and 65 (reference) and setting it to 100 has little benefit.

Note: This PR leaves the default effort at 0, because the default lossy_quality is 0.7. Therefore there will be no impact to most users. However, anyone using a higher value for the lossy_quality will notice a significant increase in the time it takes to create the VRAM compressed files. As an indication, here are the times in ms I get for importing a 1024x1024 texture to ETC and ETC2 format with this PR:

Lossy Quality	ETC	ETC2
0.7	797	1,452
> 0.75	4,104	9,284
> 0.85	11,419	36,787
> 0.95	44,267	73,894

The benefit of course is that the textures will have the expected higher quality; even if the artificial adjustment to the effort remains.

[akien-mga]

Thanks!