thermal: prevent another potential overflow

Switch to snprintf just like: aosp-mirror/kernel_common@b55f0a9f865be75ca1019aad331f3225f7b50ce8

[Upstream commit: aosp-mirror/kernel_common@c99626092efca3061b387043d4a7399bf75fbdd5]
Fixes: aosp-mirror/kernel_common@203d3d4aa482339b4816f131f713e1b8ee37f6dd [the generic thermal sysfs driver]

Signed-off-by: Harshit Jain <reach@harsh1998.dev>