drm/amd/pm/powerplay/hwmgr/smu7_thermal: Prevent division by zero

drm/amd/pm/powerplay/hwmgr/smu7_thermal: Prevent division by zero

commit 7c246a05df51c52fe0852ce56ba10c41e6ed1f39 upstream.

The user can set any speed value.
If speed is greater than UINT_MAX/8, division by zero is possible.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: c52dcf49195d ("drm/amd/pp: Avoid divide-by-zero in fan_ctrl_set_fan_speed_rpm")
Signed-off-by: Denis Arefev <arefev@swemel.ru>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>