realtek: mdio: fix non-debug SerDes builds

The new SerDes mdio driver produces the following compilation
error in non-debug builds.

drivers/net/mdio/mdio-realtek-otto-serdes.c:72:12:
error: 'rtsds_sds_to_mmd' defined but not used [-Werror=unused-function]
   72 | static int rtsds_sds_to_mmd(int sds_page, int sds_regnum)
      |            ^~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Move the function into the debug section.

Fixes: 7a7ee72c4d306e7 ("realtek: mdio: add SerDes driver")
Signed-off-by: Markus Stockhausen <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20078
Signed-off-by: Robert Marko <[email protected]>

target/linux/realtek/files-6.12/drivers/net/mdio/mdio-realtek-otto-serdes.c

@@ -69,12 +69,6 @@ static bool rtsds_mmd_to_sds(struct rtsds_ctrl *ctrl, int addr, int devad, int m
 		 devad != MDIO_MMD_VEND1);
 }
 
-static int rtsds_sds_to_mmd(int sds_page, int sds_regnum)
-{
-	return FIELD_PREP(RTSDS_MMD_PAGE_MASK, sds_page) |
-	       FIELD_PREP(RTSDS_MMD_REG_MASK, sds_regnum);
-}
-
 static int rtsds_get_backing_sds(int sds, int page)
 {
 	/* non RTL931x devices have 1:1 frontend/backend mapping */
@@ -114,6 +108,12 @@ static const char * const rtsds_page_name[RTSDS_DBG_PAGE_NAMES] = {
 	[46] = "ANA_10G",	[47] = "ANA_10G_EXT",
 };
 
+static int rtsds_sds_to_mmd(int sds_page, int sds_regnum)
+{
+	return FIELD_PREP(RTSDS_MMD_PAGE_MASK, sds_page) |
+	       FIELD_PREP(RTSDS_MMD_REG_MASK, sds_regnum);
+}
+
 static int rtsds_dbg_registers_show(struct seq_file *seqf, void *unused)
 {
 	struct rtsds_debug_info *dbg_info = seqf->private;