bcache: work around a __bitwise to bool conversion sparse warning

Sparse is a bit dumb about bitwise operation on __bitwise types used
in boolean contexts.  Add a !! to explicitly propagate to boolean
without a warning.

Fixes: fcf865e3 ("block: convert features and flags to __bitwise types")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Kent Overstreet <kent.overstreet@linux.dev>
Link: https://lore.kernel.org/r/20240628131657.667797-1-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>