gcc may detect a false positive on nvme using an unintialized variable
if setting features fails. Since this is not a fast path, explicitly
initialize this variable to suppress the warning.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>