fixup: warning on clippy (src/kernlog.rs)

[pheiduck]

This PR will fix the warning which is often showing on the CI

error: temporary with significant drop in match scrutinee
--> src/kernlog.rs:71:19
|
71|            match kmsg.as_mut() {
| ^^^^^^^^^^^^^

[pheiduck]

@keszybz @ignatenkobrain I think we can merge this? - Do you reviewed my changes what do think?

[nabijaczleweli]

Applied as 1f822112c3dd8689d919c507ae8ca1bd911618b5 with minor editorial

[pheiduck]

Thanks!