bcachefs: split error messages of invalid compression into two lines

bcachefs: split error messages of invalid compression into two lines

When an invalid compression type or level is passed as an argument
to `--compression`, two error messages are squashed into one line:

    > bcachefs format --compression=lzo bcachefs-comp.img
    invalid option: invalid compression typecompression: parse error

    > bcachefs format --compression=lz4:16 bcachefs-comp.img
    invalid option: invalid compression levelcompression: parse error

To resolve this issue, add a newline character at the end of the
first error message to separate them into two lines.

Signed-off-by: Integral <integral@archlinuxcn.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>