thermal: ti-soc-thermal: remove usage of IS_ERR_OR_NULL

This patch changes the driver to avoid the usage of IS_ERR_OR_NULL()
macro. This macro can lead to dangerous results, like returning
success (0) during a failure scenario (NULL pointer handling).

For this reason this patch is changing the driver after
revisiting the code. These are the cases:
i. For cases in which IS_ERR_OR_NULL() is used for checking
return values of functions that returns either PTR_ERR()
or a valid pointer, it has been translated to IS_ERR() check only.
ii. For cases that a NULL check is still needed, it has been
translated to if (!ptr || IS_ERR(ptr)).

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>