staging: sm7xxfb: fix struct names related to vesa modes

This patch renames structs related to vesa modes in order to get more
readable code on sm712vga_setup.

Tested with SM712.

Signed-off-by: Javier M. Mellid <jmunhoz@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>