powerpc/amigaone: Make amigaone_discover_phbs() static

It's only used in setup.c, so make it static.

Fixes: 053d58c8 ("powerpc/amigaone: Move PHB discovery")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210210130804.3190952-3-mpe@ellerman.id.au

arch/powerpc/platforms/amigaone/setup.c

@@ -70,7 +70,7 @@ void __init amigaone_setup_arch(void)
 		ppc_md.progress("Linux/PPC "UTS_RELEASE"\n", 0);
 }
 
-void __init amigaone_discover_phbs(void)
+static void __init amigaone_discover_phbs(void)
 {
 	struct device_node *np;
 	int phb = -ENODEV;