[PATCH] powerpc: Mark the variable earlycon_acpi_spcr_enable maybe_unused

[Mathieu Malaterre <malat@debian.org>]

Re-use the object-like macro EARLYCON_USED_OR_UNUSED to mark
`earlycon_acpi_spcr_enable` as maybe_unused.

Fix the following warning (treated as error in W=1)

  CC      arch/powerpc/kernel/setup-common.o
In file included from ./include/linux/serial_8250.h:14:0,
                 from arch/powerpc/kernel/setup-common.c:33:
./include/linux/serial_core.h:382:19: error: ‘earlycon_acpi_spcr_enable’ defined but not used [-Werror=unused-const-variable=]
 static const bool earlycon_acpi_spcr_enable;
                   ^~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Signed-off-by: Mathieu Malaterre <malat@debian.org>
---
 include/linux/serial_core.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index b32df49a3bd5..1d356105f25a 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -379,7 +379,7 @@ extern int of_setup_earlycon(const struct earlycon_id *match,
 extern bool earlycon_acpi_spcr_enable __initdata;
 int setup_earlycon(char *buf);
 #else
-static const bool earlycon_acpi_spcr_enable;
+static const bool earlycon_acpi_spcr_enable EARLYCON_USED_OR_UNUSED;
 static inline int setup_earlycon(char *buf) { return 0; }
 #endif
 
-- 
2.11.0