realtek: use correct CAUSEF_DC macro in prom.c

The workaround for an already-enabled R4K timer used a non-existent
macro CAUSE_DC. Fix compiling by using the actual macro CAUSEF_DC.

Fixes: b7aab1958591 ("realtek: SMP handling of R4K timer interrupts")
Signed-off-by: Sander Vanheule <[email protected]>

target/linux/realtek/files-5.10/arch/mips/rtl838x/prom.c

@@ -43,7 +43,7 @@ static void rtl_init_secondary(void)
  * handler that leads to continuous unhandeled interrupts. In this case disable
  * counting (DC) in the core and confirm a pending interrupt.
  */
-	write_c0_cause(read_c0_cause() | CAUSE_DC);
+	write_c0_cause(read_c0_cause() | CAUSEF_DC);
 	write_c0_compare(0);
 #endif /* CONFIG_CEVT_R4K */
 /*