uf2conv.py : wrong assert in calculation of upper address of hex format

[elfmimi]

uf2/utils/uf2conv.py

Line 180 in 3016aec

assert (upper & 0xffff) == 0

instead segment address must be multiplied by 16 and added to each subsequent data record address.

cf. https://en.wikipedia.org/wiki/Intel_HEX

[mmoskal]

Not sure what this assert was doing there. The code already multiplies by 16 (by doing << 4). Thanks!