Awkward error message

[CramBL]

This leads to error messages such as Not valid packet's checksum, expect 0x8ff, got 0x216b which sounds awkward.

Would be better as Invalid packet checksum: expected 0x8ff, got 0x216b

https://github.com/ublox-rs/ublox/blob/b9f6ea1cec6011646932bd7bd24ced37009920d0/ublox/src/error.rs#L48