ste_dma40: Delete another unnecessary check in d40_probe()

A single jump label was used by the d40_probe() function in several cases
for error handling which was a bit inefficient here.

* This implementation detail could be improved by the introduction
  of another jump label.

* Remove an extra check for the variable "base".

* Omit its explicit initialisation at the beginning then.

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