drm/nouveau/hwmon: Use sysfs_emit in show function callsbacks

According to Documentation/filesystems/sysfs.rst, the show() callback
function of kobject attributes should strictly use sysfs_emit() instead
of sprintf() family functions. So, make this change.
Issue identified using the coccinelle device_attr_show.cocci script.

Signed-off-by: Deepak R Varma <drv@mailo.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/Y/+pDaHOgG1x8Py2@ubun2204.myguest.virtualbox.org