ufs: Use 'TASK_TAG' to construct the ucd_req_ptr->header.dword_0

Instead of using the hard-coded value of 0x1f, use 'TASK_TAG'
macro instead to construct the ucd_req_ptr->header.dword_0

This is in sync with what the Linux UFS driver does, i.e.
set the byte0 equal to TASK_TAG (see [1]).

Setting it to a fixed value of 0x1f is wrong as we define
TASK_TAG as 0 inside u-boot ufs framework. So, instead we
should  use the macro value directly.

[1]. https://github.com/torvalds/linux/blob/master/drivers/ufs/core/ufshcd.c#L2705

Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
diff --git a/drivers/ufs/ufs.c b/drivers/ufs/ufs.c
index 8dd29ed..3bf1a95 100644
--- a/drivers/ufs/ufs.c
+++ b/drivers/ufs/ufs.c
@@ -775,7 +775,7 @@
 
 	/* command descriptor fields */
 	ucd_req_ptr->header.dword_0 =
-			UPIU_HEADER_DWORD(UPIU_TRANSACTION_NOP_OUT, 0, 0, 0x1f);
+			UPIU_HEADER_DWORD(UPIU_TRANSACTION_NOP_OUT, 0, 0, TASK_TAG);
 	/* clear rest of the fields of basic header */
 	ucd_req_ptr->header.dword_1 = 0;
 	ucd_req_ptr->header.dword_2 = 0;