clock_imx8mq: Make do_imx8m_showclocks() static

Since do_imx8m_showclocks() is only used inside this file, make it 'static'.

This fixes the following sparse warning:

arch/arm/mach-imx/imx8m/clock_imx8mq.c:836:5: warning: no previous prototype
 for ‘do_imx8m_showclocks’ [-Wmissing-prototypes]
 int do_imx8m_showclocks(cmd_tbl_t *cmdtp, int flag, int argc,
     ^~~~~~~~~~~~~~~~~~~

Signed-off-by: Pedro Jardim <jardim.c.pedro@gmail.com>
diff --git a/arch/arm/mach-imx/imx8m/clock_imx8mq.c b/arch/arm/mach-imx/imx8m/clock_imx8mq.c
index 663fe4d..d8530cc 100644
--- a/arch/arm/mach-imx/imx8m/clock_imx8mq.c
+++ b/arch/arm/mach-imx/imx8m/clock_imx8mq.c
@@ -811,7 +811,7 @@
  * Dump some clockes.
  */
 #ifndef CONFIG_SPL_BUILD
-int do_imx8m_showclocks(cmd_tbl_t *cmdtp, int flag, int argc,
+static int do_imx8m_showclocks(cmd_tbl_t *cmdtp, int flag, int argc,
 		       char * const argv[])
 {
 	u32 freq;