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Incorrect hsync pulse width on 640x480@60 and others, due to incorrect hsync_start rounding

When I run cvt 640 480 60, I get result:

# 640x480 59.38 Hz (CVT 0.31M3) hsync: 29.69 kHz; pclk: 23.75 MHz
Modeline "640x480_60.00"   23.75  640 664 720 800  480 483 487 500 -hsync +vsync

The hsync start position of 664 is incorrect; it should be 656, matching the PDF spec, spreadsheet calculator, and https://tomverbeure.github.io/video_timings_calculator.

This bug arises because you calculate hsync_start using (link):

        mode_info->hsync_start = mode_info->hsync_end -
            (mode_info->htotal * CVT_HSYNC_PERCENTAGE) / 100;
        mode_info->hsync_start += CVT_H_GRANULARITY -
            mode_info->hsync_start % CVT_H_GRANULARITY;

The problem is that when hsync_start starts out as a multiple of 8, this code erroneously adds 8 to it when "rounding up" to a multiple of 8. Instead the value should remain unchanged.

This bug can be fixed by replacing those lines with:

        {
            int hsync_w = (mode_info->htotal * CVT_HSYNC_PERCENTAGE) / 100;
            hsync_w -= hsync_w % CVT_H_GRANULARITY;
            mode_info->hsync_start = mode_info->hsync_end - hsync_w;
        }

Should I file a pull request?

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