docs(xilinx): correct function description

Inside pm_ipi.c file, corrected the function description of
pm_ipi_buff_read_callb() and removed the return type as this is a void
function.

Signed-off-by: Naman Patel <naman.patel@amd.com>
Change-Id: I6257894337ef64497afb3e80d70af91a20357d5f
diff --git a/plat/xilinx/common/pm_service/pm_ipi.c b/plat/xilinx/common/pm_service/pm_ipi.c
index 513d6be..a3c3a6f 100644
--- a/plat/xilinx/common/pm_service/pm_ipi.c
+++ b/plat/xilinx/common/pm_service/pm_ipi.c
@@ -172,12 +172,13 @@
 }
 
 /**
- * pm_ipi_buff_read_callb() - Reads IPI response after remote processor has
- *			      handled interrupt
- * @value	Used to return value from IPI buffer element (optional)
+ * pm_ipi_buff_read_callb() - Callback function that reads value from
+ *			      ipi response buffer
+ * @value	Used to return value from IPI buffer element
  * @count	Number of values to return in @value
  *
- * @return	Returns status, either success or error+reason
+ * This callback function fills requested data in @value from ipi response
+ * buffer.
  */
 void pm_ipi_buff_read_callb(uint32_t *value, size_t count)
 {