IB/usnic: Remove '0x' when using %pa format

%pa format already prints in hexadecimal format, so remove the '0x' annotation
to avoid a double '0x0x' pattern.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>