clk.h: inline clk_get_by_name()

Fix compile warning for non OF_CONTROL builds:

---8<---
In file included from /Volumes/devel/u-boot/drivers/gpio/atmel_pio4.c:10:0:
/Volumes/devel/u-boot/include/clk.h:107:12: warning: 'clk_get_by_name' defined but not used [-Wunused-function]
--->8---

Signed-off-by: Andreas Bießmann <andreas@biessmann.org>
Acked-by: Stephen Warren <swarren@nvidia.com>
diff --git a/include/clk.h b/include/clk.h
index 161bc28..dc18b03 100644
--- a/include/clk.h
+++ b/include/clk.h
@@ -104,7 +104,7 @@
 	return -ENOSYS;
 }
 
-static int clk_get_by_name(struct udevice *dev, const char *name,
+static inline int clk_get_by_name(struct udevice *dev, const char *name,
 			   struct clk *clk)
 {
 	return -ENOSYS;