start.cold/warm: Correct MSR instructions (#42)

The second operand needs to be an immediate

exosphere/start.cold.s

@@ -10,7 +10,7 @@ __start_cold:
         */
     /* The following comments are mine. */
     /* mask all interrupts */
-    msr daifset, daif
+    msr daifset, 0b1111
 
     /*
         Enable invalidates of branch target buffer, then flush

exosphere/start.warm.s

@@ -10,7 +10,7 @@ __start_warm:
         */
     /* The following comments are mine. */
     /* mask all interrupts */
-    msr daifset, daif
+    msr daifset, 0b1111
 
     /*
         Enable invalidates of branch target buffer, then flush