stlink_probe.read_memory_block8 returning extra bytes on un-aligned 1 byte read

[pdietl]

It seems to me that commit 46f1ac66c26169270b6c6e3d7992f3b106a8077b introduced a bug. The function stlink_probe.read_memory_block8 will return an array with two bytes in it if the addressed is aligned on a 2-byte boundary but a read of 1 byte (size=1) is requested. This ends up causing an assertion at /memory.py(263)read_memory_block8(): 0107462 E Unhandled exception in handle_message (b'v'): result size (2) != requested size (1) [gdbserver]

I assume we need to add something along the lines of array[0] somewhere, though I am not sure about the appropriate place.

@flit