[MIPS] Fix modpost warning.

WARNING: vmlinux.o(.text+0x1718): Section mismatch: reference to .init.text:mipsmt_build_cpu_map (between 'plat_smp_setup' and 'prom_init_secondary')
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/mips-boards/malta/malta_smtc.c

@@ -58,7 +58,7 @@ void prom_init_secondary(void)
  * but it may be multithreaded.
  */
 
-void plat_smp_setup(void)
+void __cpuinit plat_smp_setup(void)
 {
 	if (read_c0_config3() & (1<<2))
 		mipsmt_build_cpu_map(0);