s2io: Fix warnings due to -Wunused-but-set-variable.

Most of these are cases where we are trying to read back a register
after a write to ensure completion.

Simply pre-fixing the readl() or readq() with "(void)" is sufficient
because these are volatile operations and the compiler cannot eliminate
them just because no real assignment takes place.

The case of free_rxd_blk()'s assignments to "struct buffAdd *ba" is a
real spurious assignment as this variable is completely otherwise
unused.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Jon Mason <jdmason@kudzu.us>