pci: Handle failed calloc in decode_regions()

Add a check for calloc() failing to allocate the requested memory.

Make decode_regions() return an error code.

Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Reviewed-by: Stefan Roese <sr@denx.de>