IB: Remove useless ibdev_is_alive() tests from sysfs code

Some attribute show functions test ibdev_is_alive() to make sure that
it's OK to access device state.  However, the sysfs attributes will
not be registered until the device is fully initialized, and they'll
be unregistered before anything is torn down, so ibdev_is_alive()
doesn't do anything useful.  Remove it.

Signed-off-by: Roland Dreier <rolandd@cisco.com>