nimble/phy: Fix timings for LE Coded
nimble/phy: Fix timings for LE Coded

e8f9ecca changed values for S2 and S8 phy modes. This did not affect LL
code since it was using symbols everywhere, however in nRF52 PHY timings
are indexed by raw values so LE Coded timings are now used incorrectly.

To avoid such issues in future, let's just index arrays with timings
using proper symbols.

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