Linux 3.13: Check return value from bdi_init

Linux 3.13: Check return value from bdi_init

The use of the bdi_init function now gets a warning because the
return value is unused and the function is now defined with
the warn_unused_result attribute.

Assign and check the return value.

Reviewed-on: http://gerrit.openafs.org/10530
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit ccc5d3f7adceda4d8cf41f04fe02d5cfe376befd)

Change-Id: I2ccd9bbdce396a003030e3e09f9f6d75a1c4fa7c
Reviewed-on: https://gerrit.openafs.org/12274
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Tested-by: Stephan Wiesand <stephan.wiesand@desy.de>