Padding of registers with non 8-bit multiple sizes is incorrectly generated

[david-sawatzke]

See im-tomu/fomu-pac-rs#1, seems to stem from

svd2rust/src/generate/peripheral.rs

Line 326 in 325a304

let field_end = field_start + field.size / BITS_PER_BYTE;

truncating instead of rounding up.

[david-sawatzke]

Fixed in #419