[PATCH -next] serial: stm32: Fix unused-variable warning

[Ren Zhijie]

If CONFIG_SERIAL_EARLYCON and CONFIG_OF are both not set,
gcc warns about unused variable:

drivers/tty/serial/stm32-usart.c:83:32: error: ‘stm32h7_info’ defined but not used [-Werror=unused-variable]
 static struct stm32_usart_info stm32h7_info = {
                                ^~~~~~~~~~~~
drivers/tty/serial/stm32-usart.c:61:32: error: ‘stm32f7_info’ defined but not used [-Werror=unused-variable]
 static struct stm32_usart_info stm32f7_info = {
                                ^~~~~~~~~~~~
drivers/tty/serial/stm32-usart.c:40:32: error: ‘stm32f4_info’ defined but not used [-Werror=unused-variable]
 static struct stm32_usart_info stm32f4_info = {
                                ^~~~~~~~~~~~
cc1: all warnings being treated as errors

Mark these variables as __maybe_unused  to fix this.

Fixes: c7039ce904c0 ("serial: stm32: make info structs static to avoid sparse warnings")
Signed-off-by: Ren Zhijie <renzhijie2 at huawei.com>
---
 drivers/tty/serial/stm32-usart.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 0b18615b2ca4..22013b12f471 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -37,7 +37,7 @@
 
 
 /* Register offsets */
-static struct stm32_usart_info stm32f4_info = {
+static struct stm32_usart_info __maybe_unused stm32f4_info = {
 	.ofs = {
 		.isr	= 0x00,
 		.rdr	= 0x04,
@@ -58,7 +58,7 @@ static struct stm32_usart_info stm32f4_info = {
 	}
 };
 
-static struct stm32_usart_info stm32f7_info = {
+static struct stm32_usart_info __maybe_unused stm32f7_info = {
 	.ofs = {
 		.cr1	= 0x00,
 		.cr2	= 0x04,
@@ -80,7 +80,7 @@ static struct stm32_usart_info stm32f7_info = {
 	}
 };
 
-static struct stm32_usart_info stm32h7_info = {
+static struct stm32_usart_info __maybe_unused stm32h7_info = {
 	.ofs = {
 		.cr1	= 0x00,
 		.cr2	= 0x04,
-- 
2.17.1