serial: 8250: omap: Move uart_write() inside PM section

If CONFIG_PM is not set (e.g. m68k/allmodconfig):

    drivers/tty/serial/8250/8250_omap.c:169:13: error: ‘uart_write’ defined but not used [-Werror=unused-function]
      169 | static void uart_write(struct omap8250_priv *priv, u32 reg, u32 val)
	  |             ^~~~~~~~~~

Fix tis by moving uart_write() inside the existing section protected
by #ifdef CONFIG_PM.

Reported-by: noreply@ellerman.id.au
Link: http://kisskb.ellerman.id.au/kisskb/buildresult/14925095/
Fixes: 398cecc2 ("serial: 8250: omap: Fix imprecise external abort for omap_8250_pm()")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20230515065706.1723477-1-geert@linux-m68k.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_omap.c

@@ -166,11 +166,6 @@ static u32 uart_read(struct omap8250_priv *priv, u32 reg)
 	return readl(priv->membase + (reg << OMAP_UART_REGSHIFT));
 }
 
-static void uart_write(struct omap8250_priv *priv, u32 reg, u32 val)
-{
-	writel(val, priv->membase + (reg << OMAP_UART_REGSHIFT));
-}
-
 /*
  * Called on runtime PM resume path from omap8250_restore_regs(), and
  * omap8250_set_mctrl().
@@ -1666,6 +1661,11 @@ static int omap8250_lost_context(struct uart_8250_port *up)
 	return 0;
 }
 
+static void uart_write(struct omap8250_priv *priv, u32 reg, u32 val)
+{
+	writel(val, priv->membase + (reg << OMAP_UART_REGSHIFT));
+}
+
 /* TODO: in future, this should happen via API in drivers/reset/ */
 static int omap8250_soft_reset(struct device *dev)
 {