drivers: thermal: tsens: Work with old DTBs

In order for the old DTBs to continue working, the new interrupt code
must not return an error if interrupts are not defined. Don't return an
error in case of -ENXIO.

Fixes: 634e11d5 ("drivers: thermal: tsens: Add interrupt support")
Suggested-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/cea3317c5d793db312064d68b261ad420a4a81b1.1576146898.git.amit.kucheria@linaro.org