powerpc/44x: Make ppc44x_idle_init() static

The 44x/fsp2_defconfig build fails with:

arch/powerpc/platforms/44x/idle.c:30:12: error: no previous prototype for ‘ppc44x_idle_init’ [-Werror=missing-prototypes]
30 | int __init ppc44x_idle_init(void)
| ^~~~~~~~~~~~~~~~

Fix it by making ppc44x_idle_init() static.

Reviewed-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://msgid.link/[e-mail]

arch/powerpc/platforms/44x/idle.c

···
 	isync();
 }
 
-int __init ppc44x_idle_init(void)
+static int __init ppc44x_idle_init(void)
 {
 	if (!mode_spin) {
 		/* If we are not setting spin mode