network-manager: S45network-manager: don't use pidof -o option

The pidof -o option is only available in the Busybox applet if
CONFIG_FEATURE_PIDOF_OMIT is enabled, and it isn't really needed here as the
init script isn't called 'NetworkManager', so get rid of it.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>