drm/i915/hwmon: Fix static analysis tool reported issues

Updated i915 hwmon with fixes for issues reported by static analysis tool.
Fixed integer overflow with upcasting.

v2:
- Added Fixes tag (Badal).
- Updated commit message as per review comments (Anshuman).

Fixes: 4c2572fe ("drm/i915/hwmon: Expose power1_max_interval")
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Karthik Poosa <karthik.poosa@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231204144809.1518704-1-karthik.poosa@intel.com