MIPS: PNX8550: Fix section mismatch

Triggered by pnx8550-jbs_defconfig and pnx8550-stb810_defconfig:

WARNING: vmlinux.o(.text+0xc0c): Section mismatch in reference from the function prom_getcmdline() to the variable .init.data:arcs_cmdline
The function prom_getcmdline() references
the variable __initdata arcs_cmdline.
This is often because prom_getcmdline lacks a __initdata
annotation or the annotation of arcs_cmdline is wrong.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/pnx8550/common/prom.c

@@ -30,7 +30,7 @@ typedef struct
 }t_env_var;
 
 
-char * prom_getcmdline(void)
+char * __init prom_getcmdline(void)
 {
 	return &(arcs_cmdline[0]);
 }