fs/9p: Use mknod 9p operation on create without open request

A create without LOOKUP_OPEN flag set is due to mknod of regular
files. Use mknod 9P operation for the same

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>