Blackfin: just set SP register directly during init

No need to set the SP register indirectly to the configured value when it
can be set directly.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

cpu/blackfin/start.S

@@ -163,9 +163,8 @@ ENTRY(_start)
 .Lnorelocate:
 
 	/* Setup the actual stack in external memory */
-	r0.h = HI(CONFIG_STACKBASE);
-	r0.l = LO(CONFIG_STACKBASE);
-	sp = r0;
+	sp.h = HI(CONFIG_STACKBASE);
+	sp.l = LO(CONFIG_STACKBASE);
 	fp = sp;
 
 	/* Now lower ourselves from the highest interrupt level to