netfs: Fix is-caching check in read-retry

netfs: Fix is-caching check in read-retry

The read-retry code checks the NETFS_RREQ_COPY_TO_CACHE flag to determine
if there might be failed reads from the cache that need turning into reads
from the server, with the intention of skipping the complicated part if it
can.  The code that set the flag, however, got lost during the read-side
rewrite.

Fix the check to see if the cache_resources are valid instead.  The flag
can then be removed.

Fixes: ee4cdf7b ("netfs: Speed up buffered reading")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/3752048.1734381285@warthog.procyon.org.uk


cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>