NFSD: Avoid calling fh_drop_write() twice in do_nfsd_create()

Clean up: The "out" label already invokes fh_drop_write().

Note that fh_drop_write() is already careful not to invoke
mnt_drop_write() if either it has already been done or there is
nothing to drop. Therefore no change in behavior is expected.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>