fs/9p: remove unnecessary invalidate_inode_pages2

There was an invalidate_inode_pages2 added to readonly mmap path
that is unnecessary since that path is only entered when writeback
cache is disabled on mount.

Cc: stable@vger.kernel.org
Fixes: 1543b4c ("fs/9p: remove writeback fid and fix per-file modes")
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>

fs/9p/vfs_file.c

@@ -506,7 +506,6 @@ v9fs_file_mmap(struct file *filp, struct vm_area_struct *vma)
 
 	if (!(v9ses->cache & CACHE_WRITEBACK)) {
 		p9_debug(P9_DEBUG_CACHE, "(read-only mmap mode)");
-		invalidate_inode_pages2(filp->f_mapping);
 		return generic_file_readonly_mmap(filp, vma);
 	}