[PATCH v2] clk: fix clk_get_rate() documentation

[Giulio Benetti]

Improve clk_get_rate() @return documentation that otherwise is a bit
ambiguous. At the moment I expect to return 0 as error since the return
type is 'ulong', instead the function really returns negative value in
case the corresponding function pointer is null and returns 0 if the clock
is invalid.

Signed-off-by: Giulio Benetti <giulio.benetti at benettiengineering.com>
---
V1->V2:
* previous comment was wrong, this function returns negative value, so let's
  improve it's @return documentation as suggested by Simon Glass
---
 include/clk.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/clk.h b/include/clk.h
index ca6b85fa6f..5a8c7244d0 100644
--- a/include/clk.h
+++ b/include/clk.h
@@ -344,7 +344,8 @@ int clk_free(struct clk *clk);
  *
  * @clk:	A clock struct that was previously successfully requested by
  *		clk_request/get_by_*().
- * @return clock rate in Hz, or -ve error code.
+ * @return clock rate in Hz on success, 0 for invalid clock, or -ve error code
+ *	   for other errors.
  */
 ulong clk_get_rate(struct clk *clk);
 
-- 
2.25.1