boston: Drop unused return value

The boston lowlevel_init() function zeroes the return register v0,
despite the function not being expected to return a value & that value
never being used.

Remove the redundant assignment to v0.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/board/imgtec/boston/lowlevel_init.S b/board/imgtec/boston/lowlevel_init.S
index 0c01aa9..46c9c1d 100644
--- a/board/imgtec/boston/lowlevel_init.S
+++ b/board/imgtec/boston/lowlevel_init.S
@@ -34,7 +34,6 @@
 	PTR_LA	a0, msg_ddr_ok
 	bal	lowlevel_display
 
-	move	v0, zero
 	jr	s0
 	END(lowlevel_init)