[otbn] Flop address bits to select 32-bit word in LSU
[otbn] Flop address bits to select 32-bit word in LSU

Previously the LSU relied upon the controller keeping the incoming
address stable the cycle following a load request so base word loads
could select the correct word from the WLEN data. When the load uses the
call stack as a base address register this is violated. Flopping the
bits for the word select avoids the need for the controller to keep the
address stable.

Fixes #6295

Signed-off-by: Greg Chadwick <3e4c3d6d87c017d1a2fa161477653b4039c6b2fb@lowrisc.org>

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