drivers: sensor: paj7620: Fix potential integer overflow in driver

Fix Coverity issue CID 524766: A potential integer overflow could occur
in paj7620_set_sampling_rate() due to multiplication of
sensor_value->val1 instance(which is of type int32_t) with 1000000
without typecasting it to int64_t.

Fixes #90482

Signed-off-by: Aditya Chopra <adityachopra2912@gmail.com>