docs: admin-guide: bootconfig: Fix feils to fails

s/feils/fails/p

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210107125610.1576368-1-unixbhaskar@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>