i2c: designware: Mark dw_i2c_plat_{suspend,resume}() as __maybe_unused

When CONFIG_PM is set but CONFIG_PM_SLEEP is not, two compiler warnings
appear:

  drivers/i2c/busses/i2c-designware-platdrv.c:444:12: error: unused function 'dw_i2c_plat_suspend' [-Werror,-Wunused-function]
  static int dw_i2c_plat_suspend(struct device *dev)
             ^
  drivers/i2c/busses/i2c-designware-platdrv.c:465:12: error: unused function 'dw_i2c_plat_resume' [-Werror,-Wunused-function]
  static int dw_i2c_plat_resume(struct device *dev)
             ^
  2 errors generated.

These functions are only used in SET_LATE_SYSTEM_SLEEP_PM_OPS(), which
is defined as empty when CONFIG_PM_SLEEP is not defined. Mark the
functions as __maybe_unused to make it clear that these functions might
be unused in this configuration.

Fixes: c57813b8 ("i2c: designware: Lock the adapter while setting the suspended flag")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-designware-platdrv.c

@@ -441,7 +441,7 @@ static int dw_i2c_plat_runtime_suspend(struct device *dev)
 	return 0;
 }
 
-static int dw_i2c_plat_suspend(struct device *dev)
+static int __maybe_unused dw_i2c_plat_suspend(struct device *dev)
 {
 	struct dw_i2c_dev *i_dev = dev_get_drvdata(dev);
 
@@ -462,7 +462,7 @@ static int dw_i2c_plat_runtime_resume(struct device *dev)
 	return 0;
 }
 
-static int dw_i2c_plat_resume(struct device *dev)
+static int __maybe_unused dw_i2c_plat_resume(struct device *dev)
 {
 	struct dw_i2c_dev *i_dev = dev_get_drvdata(dev);