drm/amd/pm: Prevent divide by zero

divide error: 0000 [#1] SMP PTI
CPU: 3 PID: 78925 Comm: tee Not tainted 5.15.50-1-lts #1
Hardware name: MSI MS-7A59/Z270 SLI PLUS (MS-7A59), BIOS 1.90 01/30/2018
RIP: 0010:smu_v11_0_set_fan_speed_rpm+0x11/0x110 [amdgpu]

Speed is user-configurable through a file.
I accidentally set it to zero, and the driver crashed.
Reviewed-by: NEvan Quan <evan.quan@amd.com>
Reviewed-by: NAndré Almeida <andrealmeid@igalia.com>
Signed-off-by: NYefim Barashkin <mr.b34r@kolabnow.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/swsmu/smu11/smu_v11_0.c

@@ -1228,6 +1228,8 @@ int smu_v11_0_set_fan_speed_rpm(struct smu_context *smu,
 	uint32_t crystal_clock_freq = 2500;
 	uint32_t tach_period;
 
+	if (speed == 0)
+		return -EINVAL;
 	/*
 	 * To prevent from possible overheat, some ASICs may have requirement
 	 * for minimum fan speed: