video: fbdev: atari: Fix VGA modes

The pixclock values in the vga and vga70 modes are wrong, as they should
use the 25.175 MHz clock instead of the 32 MHz clock.
Swap the left and right margins to match f25.{right,left} (struct
pixel_clock declares them in a different order), and update the hsync
lengths to match what the driver programs by default.
Correct the (wrong) floating-point vrefresh value for the vga mode.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>