[PATCH v2 -next] hwmon: (pmbus) fix build error unused-function

[Ren Zhijie]

If CONFIG_PMBUS is y and CONFIG_DEBUG_FS is not set.

make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-, will be failed, like this:
drivers/hwmon/pmbus/pmbus_core.c:593:13: error: ‘pmbus_check_block_register’ defined but not used [-Werror=unused-function]
 static bool pmbus_check_block_register(struct i2c_client *client, int page,
             ^~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[3]: *** [drivers/hwmon/pmbus/pmbus_core.o] Error 1
make[2]: *** [drivers/hwmon/pmbus] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [drivers/hwmon] Error 2
make[1]: *** Waiting for unfinished jobs....
make: *** [drivers] Error 2

To fix building warning, use __maybe_unused to attach this func.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Fixes: c3ffc3a1ff83("hwmon: (pmbus) add a function to check the presence of a block register")
Signed-off-by: Ren Zhijie <renzhijie2@xxxxxxxxxx>
---
v2: use __maybe_unused to attach this function, which Guenter suggested.
---
 drivers/hwmon/pmbus/pmbus_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index 809e666cb52b..e6d3a1118453 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -590,7 +590,7 @@ bool pmbus_check_word_register(struct i2c_client *client, int page, int reg)
 }
 EXPORT_SYMBOL_NS_GPL(pmbus_check_word_register, PMBUS);
 
-static bool pmbus_check_block_register(struct i2c_client *client, int page,
+static bool __maybe_unused pmbus_check_block_register(struct i2c_client *client, int page,
 				       int reg)
 {
 	int rv;
-- 
2.17.1