fs/9p: remove erroneous nlink init from legacy stat2inode

In 9p2000 legacy mode, stat2inode initializes nlink to 1,
which is redundant with what alloc_inode should have already set.
9p2000.u overrides this with extensions if present in the stat
structure, and 9p2000.L incorporates nlink into its stat structure.

At the very least this probably messes with directory nlink
accounting in legacy mode.

Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>