Revert "tracing/trigger: Fix to return error if failed to alloc snapshot"

This reverts commit 56cfbe60 which is
commit 0958b33e upstream.

The change has an incorrect assumption about the return value because
in the current stable trees for versions 5.15 and before, the following
commit responsible for making 0 a success value is not present:
b8cc44a4 ("tracing: Remove logic for registering multiple event triggers at a time")

The return value should be 0 on failure in the current tree, because in
the functions event_trigger_callback() and event_enable_trigger_func(),
we have:

	ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
	/*
	 * The above returns on success the # of functions enabled,
	 * but if it didn't find any functions it returns zero.
	 * Consider no functions a failure too.
	 */
	if (!ret) {
		ret = -ENOENT;

Cc: stable@kernel.org # 5.15, 5.10, 5.4, 4.19
Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>