__io_file_supports_nowait for regular files

[Christoph Hellwig <hch@xxxxxx>]

Hi Jens,

is there any good reason __io_file_supports_nowait checks the
blk_queue_nowait flag for regular files?  The FMODE_NOWAIT is set
for regular files that support nowait I/O, and should be all that
is needed.  Even with a block device that does not nonblocking
I/O some thing like reading from the page cache can be done
non-blocking.