[HAL][GENERIC] Update brief of HAL_GetTickFreq()

diff --git a/Src/stm32l4xx_hal.c b/Src/stm32l4xx_hal.c
index bd91e82..0c0a6ba 100644
--- a/Src/stm32l4xx_hal.c
+++ b/Src/stm32l4xx_hal.c

@@ -381,7 +381,8 @@
 
 /**
   * @brief Return tick frequency.
-  * @retval tick period in Hz
+  * @retval Tick frequency.
+  *         Value of @ref HAL_TickFreqTypeDef.
   */
 HAL_TickFreqTypeDef HAL_GetTickFreq(void)
 {