drm/radeon/radeon_pm: Convert sysfs sprintf/snprintf family to sysfs_emit

Fix the following coccicheck warning:
drivers/gpu//drm/radeon/radeon_pm.c:521:9-17: WARNING: use scnprintf or
sprintf
drivers/gpu//drm/radeon/radeon_pm.c:475:8-16: WARNING: use scnprintf or
sprintf
drivers/gpu//drm/radeon/radeon_pm.c:418:8-16: WARNING: use scnprintf or
sprintf
drivers/gpu//drm/radeon/radeon_pm.c:363:8-16: WARNING: use scnprintf or
sprintf
drivers/gpu//drm/radeon/radeon_pm.c:734:8-16: WARNING: use scnprintf or
sprintf
drivers/gpu//drm/radeon/radeon_pm.c:688:8-16: WARNING: use scnprintf or
sprintf
drivers/gpu//drm/radeon/radeon_pm.c:704:8-16: WARNING: use scnprintf or
sprintf
drivers/gpu//drm/radeon/radeon_pm.c:755:8-16: WARNING: use scnprintf or
sprintf

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>