platform/x86: panasonic-laptop: Return errno correctly in show callback

platform/x86: panasonic-laptop: Return errno correctly in show callback

[ Upstream commit 5c7bebc1a3f0661db558d60e14dde27fc216d9dc ]

When an error occurs in sysfs show callback, we should return the errno
directly instead of formatting it as the result, which produces
meaningless output and doesn't inform the userspace of the error.

Fixes: 468f96bfa3a0 ("platform/x86: panasonic-laptop: Add support for battery charging threshold (eco mode)")
Fixes: d5a81d8e864b ("platform/x86: panasonic-laptop: Add support for optical driver power in Y and W series")
Signed-off-by: Yao Zi <ziyao@disroot.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20241118064637.61832-3-ziyao@disroot.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>