net/9p: fix bug in client create for .L

We are supposed to set fid->mode to reflect the flags
that were used to open the file.  We were actually setting
it to the creation mode which is the default perms of the
file not the flags the file was opened with.

Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>
Reviewed-by: Dominique Martinet <asmadeus@codewreck.org>