[SPARC]: Add reboot_command[] extern decl to asm/system.h

Kill off some sparse warnings.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/asm-sparc64/system.h b/include/asm-sparc64/system.h
index ed91a5d..53eae09 100644
--- a/include/asm-sparc64/system.h
+++ b/include/asm-sparc64/system.h
@@ -30,6 +30,8 @@
 #define ARCH_SUN4C_SUN4 0
 #define ARCH_SUN4 0
 
+extern char reboot_command[];
+
 /* These are here in an effort to more fully work around Spitfire Errata
  * #51.  Essentially, if a memory barrier occurs soon after a mispredicted
  * branch, the chip can stop executing instructions until a trap occurs.