memory: omap-gpmc: make gpmc_clk_ticks_to_ns() static

We get 1 warning when build kernel with W=1:
drivers/memory/omap-gpmc.c:354:14: warning: no previous prototype for 'gpmc_clk_ticks_to_ns' [-Wmissing-prototypes]

In fact, this function is only used in the file in which it is declared
and don't need a declaration, but can be made static.
so this patch marks it 'static'.
Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Roger Quadros <rogerq@ti.com>

drivers/memory/omap-gpmc.c

@@ -350,8 +350,8 @@ static unsigned int gpmc_ps_to_ticks(unsigned int time_ps)
 	return (time_ps + tick_ps - 1) / tick_ps;
 }
 
-unsigned int gpmc_clk_ticks_to_ns(unsigned ticks, int cs,
-				  enum gpmc_clk_domain cd)
+static unsigned int gpmc_clk_ticks_to_ns(unsigned int ticks, int cs,
+					 enum gpmc_clk_domain cd)
 {
 	return ticks * gpmc_get_clk_period(cs, cd) / 1000;
 }