Fix usage example in kvprintf(9) and its copy in libstand(3): trailing '\n'
in bitfield argument is wrong, as it will be treated as bit 10, causing any
code printing >=10 bits with bit 10 on as having a trailing comma.

Newline (intended one) should be part of the format string (already present
in the examples).

Also fix grammar and kill EOL whitespace in comment while here.

PR: 195005
Approved by: bdrewery