kernel/params.c: align add_sysfs_param documentation with code

kernel/params.c: align add_sysfs_param documentation with code

commit 630cc2b30a42c70628368a412beb4a5e5dd71abe upstream.

This parameter is named kp, so the documentation should use that.

Fixes: 9b473de87209 ("param: Fix duplicate module prefixes")
Link: http://lkml.kernel.org/r/20170919142656.64aea59e@endymion
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>