dracut: nbd: Only complain of missing binary in hostonly mode if

rootfs is on nbd

In not hostonly mode, require_binaries will still complain.
If in hostonly mode and the module is explicitly added via -a nbd, then
install() section will still complain later:
dracut-install: ERROR: installing 'nbd-client'

Signed-off-by: Thomas Renninger <trenn@suse.de>

modules.d/95nbd/module-setup.sh

@@ -3,8 +3,6 @@
 # called by dracut
 check() {
     local _rootdev
-    # If our prerequisites are not met, fail.
-    require_binaries nbd-client || return 1
 
     # if an nbd device is not somewhere in the chain of devices root is
     # mounted on, fail the hostonly check.
@@ -15,6 +13,7 @@ check() {
         [[ -b /dev/block/$_rootdev ]] || return 1
         check_block_and_slaves is_nbd "$_rootdev" || return 255
     }
+    require_binaries nbd-client || return 1
 
     return 0
 }