mips: Use PAGE_SIZE for INIT_TASK_DATA alignment again

957b369c (mips: Use generic init_task) optimistically replaced the
PAGE_SIZE INIT_TASK_DATA alignment with THREAD_SIZE, but THREAD_SIZE
is not defined, so the linking stage breaks.
Reported-by: NIngo Molnar <mingo@kernel.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/mips/kernel/vmlinux.lds.S

@@ -72,7 +72,7 @@ SECTIONS
 	.data : {	/* Data */
 		. = . + DATAOFFSET;		/* for CONFIG_MAPPED_KERNEL */
 
-		INIT_TASK_DATA(THREAD_SIZE)
+		INIT_TASK_DATA(PAGE_SIZE)
 		NOSAVE_DATA
 		CACHELINE_ALIGNED_DATA(1 << CONFIG_MIPS_L1_CACHE_SHIFT)
 		READ_MOSTLY_DATA(1 << CONFIG_MIPS_L1_CACHE_SHIFT)