microbit_seed_random() doesn't always create a random seed when SD is running

[microbit-carlos]

Originally reported in:

• randint() not random when bluetooth enabled microsoft/pxt-microbit#5409

And debugged in:

• MakeCode randint() not random when Bluetooth enabled codal-microbit-v2#409

We might need to update it as shown in:

• https://github.com/lancaster-university/codal-microbit-v2/pull/448/files

When SD is running we think maybe we are hitting this error condition and using the default seed instead of a random one:

microbit-dal/source/core/MicroBitDevice.cpp

Lines 346 to 347 in 318c6ab

	if (result != NRF_SUCCESS)
	random_value = 0xBBC5EED;