thermal: tegra: fix static checker warning

There has a static checker warning:
warn: variable dereferenced before check 'dev' (see line 222)

Since check 'dev' is unnecessary, so remove this check.

Fixes: ee6d79f202a4 ("thermal: tegra: add thermtrip function")
Signed-off-by: Wei Ni <wni@nvidia.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>