Move bootstr_valid/bootstr_buf back into .data section.

Add comment explaining that why these must not be moved into the
.bss section.

arch/sparc64/prom/bootstr.c

@@ -9,10 +9,15 @@
 #include <linux/init.h>
 #include <asm/oplib.h>
 
+/* WARNING: The boot loader knows that these next three variables come one right
+ *          after another in the .data section.  Do not move this stuff into
+ *          the .bss section or it will break things.
+ */
+
 #define BARG_LEN  256
 int bootstr_len = BARG_LEN;
-static int bootstr_valid;
-static char bootstr_buf[BARG_LEN];
+static int bootstr_valid = 0;
+static char bootstr_buf[BARG_LEN] = { 0 };
 
 char * __init
 prom_getbootargs(void)