aoe: initialize sysminor to avoid compiler warning

aoe: initialize sysminor to avoid compiler warning

Because the minor_get and related functions use the return values for
errors, the compiler doesn't know that sysminor will always either 1) be
initialized in aoedev_by_aoeaddr by the call to minor_get, or 2) be unused
as the "goto out" is executed.

This patch avoids the compiler warning.

Signed-off-by: Ed Cashin <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>