scsi: qedf: Use designated initializer for struct qed_fcoe_cb_ops

scsi: qedf: Use designated initializer for struct qed_fcoe_cb_ops

Recent fixes to the randstruct GCC plugin allowed it to notice
that this structure is entirely function pointers and is therefore
subject to randomization, but doing so requires that it always use
designated initializers. Explicitly specify the "common" member as being
initialized. Silences:

drivers/scsi/qedf/qedf_main.c:702:9: error: positional initialization of field in 'struct' declared with 'designated_init' attribute [-Werror=designated-init]
  702 |         {
      |         ^

Fixes: 035f7f87b729 ("randstruct: Enable Clang support")
Link: https://lore.kernel.org/r/20250502224156.work.617-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>