riscv: Remove unnecessary instruction

The add instruction on risc-v can have any three sources and targets, so there
is no need for an intermediate mov.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
index f3dccdb..6b3ff99 100644
--- a/arch/riscv/cpu/start.S
+++ b/arch/riscv/cpu/start.S
@@ -359,9 +359,8 @@
 call_board_init_r:
 	jal	invalidate_icache_all
 	jal	flush_dcache_all
-	la	t0, board_init_r
-	mv	t4, t0			/* offset of board_init_r() */
-	add	t4, t4, t6		/* real address of board_init_r() */
+	la	t0, board_init_r        /* offset of board_init_r() */
+	add	t4, t0, t6		/* real address of board_init_r() */
 /*
  * setup parameters for board_init_r
  */