efi/libstub/arm: Make install_memreserve_table static

Fix the following sparse warning:

drivers/firmware/efi/libstub/arm-stub.c:68:6: warning:
symbol 'install_memreserve_table' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Link: https://lore.kernel.org/r/1587643713-28169-1-git-send-email-zou_wei@huawei.comSigned-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/efi-stub.c

@@ -65,7 +65,7 @@ static struct screen_info *setup_graphics(void)
 	return si;
 }
 
-void install_memreserve_table(void)
+static void install_memreserve_table(void)
 {
 	struct linux_efi_memreserve *rsv;
 	efi_guid_t memreserve_table_guid = LINUX_EFI_MEMRESERVE_TABLE_GUID;