vgasrc: round up save/restore size

vgasrc: round up save/restore size

When calculating the size of the buffer required for the VGA/VBE state,
round up rather than truncating when dividing the number of bytes to get
the number of 64-byte blocks. Without this modification, the save state
function will write past the end of a buffer of the size requested.

Signed-off-by: Daniel Verkamp <daniel@drv.nu>