drm/xe/hwmon: Protect hwmon rw attributes with hwmon_lock

drm/xe/hwmon: Protect hwmon rw attributes with hwmon_lock

Take hwmon_lock while accessing hwmon rw attributes. For readonly
attributes its not required to take lock as reads are protected
by sysfs layer and therefore sequential.

Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231030115618.1382200-3-badal.nilawar@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>