powerpc: Fix another bug in move of altivec code to vector.S

When moving load_up_altivec to vector.S a typo in a comment caused a
thinko setting the wrong variable.
Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/vector.S

@@ -80,10 +80,10 @@ _GLOBAL(load_up_altivec)
 	mtvscr	vr0
 	REST_32VRS(0,r4,r5)
 #ifndef CONFIG_SMP
-	/* Update last_task_used_math to 'current' */
+	/* Update last_task_used_altivec to 'current' */
 	subi	r4,r5,THREAD		/* Back to 'current' */
 	fromreal(r4)
-	PPC_STL	r4,ADDROFF(last_task_used_math)(r3)
+	PPC_STL	r4,ADDROFF(last_task_used_altivec)(r3)
 #endif /* CONFIG_SMP */
 	/* restore registers and return */
 	blr
@@ -172,7 +172,7 @@ _GLOBAL(load_up_vsx)
 	oris	r12,r12,MSR_VSX@h
 	std	r12,_MSR(r1)
 #ifndef CONFIG_SMP
-	/* Update last_task_used_math to 'current' */
+	/* Update last_task_used_vsx to 'current' */
 	ld	r4,PACACURRENT(r13)
 	std	r4,0(r3)
 #endif /* CONFIG_SMP */