selftests/livepatch: normalize sysctl error message

The livepatch kselftests rely on comparing expected and actual output
from such commands as sysctl.  A recent commit in procps-ng v4.0.0 [1]
changed sysctl's output to emit key pathnames like:

  sysctl: setting key "/proc/sys/kernel/ftrace_enabled": Device or resource busy

versus previous dotted output:

  sysctl: setting key "kernel.ftrace_enabled": Device or resource busy

The modification in output was later reverted [2], but since the change
has been tagged in procps-ng v4.0.0, update the livepatch kselftest to
handle either case.

[1] https://gitlab.com/procps-ng/procps/-/commit/6389deca5bf667f5fab5912acde78ba8e0febbc7
[2] https://gitlab.com/procps-ng/procps/-/commit/b159c198c9160a8eb13254e2b631d0035b9b542c

Reported-by: Dennis(Zhuoheng) Li <[email protected]>
Signed-off-by: Joe Lawrence <[email protected]>
Reviewed-by: Kamalesh Babulal <[email protected]>
Signed-off-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

tools/testing/selftests/livepatch/functions.sh

@@ -86,7 +86,7 @@ function set_ftrace_enabled() {
 
 	if [[ "$result" != "$1" ]] ; then
 		if [[ $can_fail -eq 1 ]] ; then
-			echo "livepatch: $err" > /dev/kmsg
+			echo "livepatch: $err" | sed 's#/proc/sys/kernel/#kernel.#' > /dev/kmsg
 			return
 		fi