ste_dma40: Less checks in d40_hw_detect_init() after error detection

Four checks could be repeated by the d40_hw_detect_init() function during
error handling even if the passed variables contained a null pointer.

* Adjust jump targets according to the Linux coding style convention.

* Call the interface "iounmap" only once at the end.

* Delete the repeated checks which became unnecessary with
  this refactoring.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>