[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-sparc/system.h b/include/asm-sparc/system.h
index 45e47c1..4e08210c 100644
--- a/include/asm-sparc/system.h
+++ b/include/asm-sparc/system.h
@@ -44,6 +44,8 @@
 
 #define SUN4M_NCPUS            4              /* Architectural limit of sun4m. */
 
+extern char reboot_command[];
+
 extern struct thread_info *current_set[NR_CPUS];
 
 extern unsigned long empty_bad_page;