iio: pressure: bmp280: fix stack leak in bmp580 trigger handler

In the Linux kernel, the following vulnerability has been resolved:

iio: pressure: bmp280: fix stack leak in bmp580 trigger handler

bmp580_trigger_handler() declares its scan buffer on the stack without

an initializer and then memcpy()s 3 bytes of 24-bit sensor data into

each 4-byte __le32 field. The high byte of comp_temp and comp_press is

left uninitialized, and the channel storagebits is 32, so two bytes of

stack are pushed to userspace per scan.

This is a regression from when the buffer lived in the private data, the

move to a stack-local struct dropped the implicit zeroing.

bme280_trigger_handler() was fixed up to handle this bug, but this

driver was not fixed because there was no padding hole, but rather a

short-fill issue.

Fix this all by just zero-initializing the structure on the stack.