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The earliest surviving references I've found seem to be from inscriptions dated to the Akkadian period (2350β2150 BCE). "miSru" certainly appears as the word for Egyptian in A Concise Dictionary of Akkadian, where the word can also mean 'border' or 'frontier'.
Interestingly (or perhaps not!), the CIA seem to have come to the same conclusion about the derivation of the Arabic name for Egypt ("Misr") in their World Factbook entry for Egypt.