video: fbdev: matroxfb: set maxvram of vbG200eW to the same as vbG200 to avoid black screen

Start from commit 11be60bd "matroxfb: add Matrox MGA-G200eW board
support", when maxvram is 0x800000, monitor become black w/ error message
said: "The current input timing is not supported by the monitor display.
Please change your input timing to 1920x1080@60Hz ...".

Fixes: 11be60bd

 ("matroxfb: add Matrox MGA-G200eW board support")
Signed-off-by: Z. Liu <liuzx@knownsec.com>
Signed-off-by: Helge Deller <deller@gmx.de>