drm/amd/pm: fix null pointer access

Writing a string without delimiters (' ', '\n', '\0') to the under
gpu_od/fan_ctrl sysfs or pp_power_profile_mode for the CUSTOM profile
will result in a null pointer dereference.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4401
Signed-off-by: Umio Yasuno <coelacanth_dream@protonmail.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/amdgpu_pm.c

@@ -1398,6 +1398,8 @@ static ssize_t amdgpu_set_pp_power_profile_mode(struct device *dev,
 			if (ret)
 				return -EINVAL;
 			parameter_size++;
+			if (!tmp_str)
+				break;
 			while (isspace(*tmp_str))
 				tmp_str++;
 		}
@@ -3645,6 +3647,9 @@ static int parse_input_od_command_lines(const char *buf,
 			return -EINVAL;
 		parameter_size++;
 
+		if (!tmp_str)
+			break;
+
 		while (isspace(*tmp_str))
 			tmp_str++;
 	}