io_uring/fdinfo: grab ctx->uring_lock around io_uring_show_fdinfo()

In the Linux kernel, the following vulnerability has been resolved:

io_uring/fdinfo: grab ctx->uring_lock around io_uring_show_fdinfo()

Not everything requires locking in there, which is why the 'has_lock'
variable exists. But enough does that it's a bit unwieldy to manage.
Wrap the whole thing in a ->uring_lock trylock, and just return
with no output if we fail to grab it. The existing trylock() will
already have greatly diminished utility/output for the failure case.

This fixes an issue with reading the SQE fields, if the ring is being
actively resized at the same time.