oss: fix O_NONBLOCK in dmasound_core

We broke O_NONBLOCK handling in OSS dmasound_core in 2.3.11-pre3 - the
original code copied f_flags to open_mode and then checked for
O_NONBLOCK in there, but that got changed to copying f_mode and
O_NONBLOCK has not reached that field in any kernel version.

Since we do not care for any other bits, the fix is obvious...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>