nimble/phy: Fix resolving address on nRF51
nimble/phy: Fix resolving address on nRF51

This is the same as 2d34c653a but for nRF51 which I forgot to change
there...

X-Original-Commit: 8ce36f00865e4c8708baba794904d30a00672343

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble