RDMA/rxe: Remove rxe_info from rxe_set_mtu

RDMA/rxe: Remove rxe_info from rxe_set_mtu

commit 9ac01f434a1e ("RDMA/rxe: Extend dbg log messages to err and info")
newly added this info. But it did only show null device when
the rdma_rxe is being loaded because dev_name(rxe->ib_dev->dev)
has not yet been assigned at the moment:

"(null): rxe_set_mtu: Set mtu to 1024"

Remove it to silent this message, check the mtu from it backend link
instead if needed.

CC: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Link: https://lore.kernel.org/r/20240109083253.3629967-2-lizhijian@fujitsu.com
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Leon Romanovsky <leon@kernel.org>