wifi: mt76: mt7925: Fix null-ptr-deref in mt7925_thermal_init()

wifi: mt76: mt7925: Fix null-ptr-deref in mt7925_thermal_init()

devm_kasprintf() returns NULL on error. Currently, mt7925_thermal_init()
does not check for this case, which results in a NULL pointer
dereference.

Add NULL check after devm_kasprintf() to prevent this issue.

Fixes: 396e41a74a88 ("wifi: mt76: mt7925: support temperature sensor")
Signed-off-by: Henry Martin <bsdhenryma@tencent.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patch.msgid.link/20250625124901.1839832-1-bsdhenryma@tencent.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>