atm: iphase: Fix set-but-not-used warnings.

The "iavcc" and "iadev" cases are obvious.

The intr_status and frmr_intr cases are reading a register to clear
the chip status.  This driver is pretty old and creaky, and uses
volatile pointer dereferences to do register I/O when it should be
using readl() and friends.  However that it outside of the scope of
these changes.

Signed-off-by: David S. Miller <davem@davemloft.net>