Unsound usages of unsafe implementation from `u8` to `DtbHeader`

[llooFlashooll]

Hi, I am scanning the hermit-dtb in the latest version with my own static analyzer tool.

Unsafe conversion found at: src/lib.rs#L136

    pub unsafe fn from_raw(address: *const u8) -> Option<Self> {
        let header = &*(address as *const DtbHeader);
        if !Self::check_header(header) {
            return None;
        }

This unsound implementation would create a misalignment issues if the type size of u8 is smaller than the type size of DtbHeader.

This would potentially cause undefined behaviors in Rust. If we further manipulate the problematic converted types, it would potentially lead to different consequences such as access out-of-bound. I am reporting this issue for your attention.