9p/vfs_super.c: Remove unused parameter data in v9fs_fill_super

v9fs_fill_super has a param 'void *data' which is unused in the
function.

This patch removes the 'void *data' param in v9fs_fill_super and changes
the parameters in all function calls of v9fs_fill_super.

Link: http://lkml.kernel.org/r/20190523165619.GA4209@bharath12345-Inspiron-5559


Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>