thermal: bcm2835: fix an error code in probe()

This causes a static checker because we're passing a valid pointer to
PTR_ERR().  "err" is already the correct error code, so we can just
delete this line.

Fixes: bcb7dd9e ("thermal: bcm2835: add thermal driver for bcm2835 SoC")
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>