x86: efi.c declare add_efi_memmap before they get used

Impact: cleanup, avoid sparse warning

Fixes this sparse warning:

  arch/x86/kernel/efi.c:67:5: warning: symbol 'add_efi_memmap' was not declared. Should it be static?

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index a2e545c..ca5ffb2 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -90,6 +90,7 @@
 
 #endif /* CONFIG_X86_32 */
 
+extern int add_efi_memmap;
 extern void efi_reserve_early(void);
 extern void efi_call_phys_prelog(void);
 extern void efi_call_phys_epilog(void);