sparc32,leon: drop leon_init()

This function was only used to set of_pdt_build_more to leon_node_init().
But the leon_node_init() was a nop as prom_amba_init was never assigned.

Cc: Daniel Hellstrom <daniel@gaisler.com>
Cc: Konrad Eisele <konrad@gaisler.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>