powerpc/process: Fix altivec SPR not being saved

In save_sprs() in process.c contains the following test:

	if (cpu_has_feature(cpu_has_feature(CPU_FTR_ALTIVEC)))
		t->vrsave = mfspr(SPRN_VRSAVE);

CPU feature with the mask 0x1 is CPU_FTR_COHERENT_ICACHE so the test
is equivilent to:

	if (cpu_has_feature(CPU_FTR_ALTIVEC) &&
		cpu_has_feature(CPU_FTR_COHERENT_ICACHE))

On CPUs without support for both (i.e G5) this results in vrsave not
being saved between context switches. The vector register save/restore
code doesn't use VRSAVE to determine which registers to save/restore,
but the value of VRSAVE is used to determine if altivec is being used
in several code paths.

Fixes: 152d523e6307 ("powerpc: Create context switch helpers save_sprs() and restore_sprs()")
Cc: stable@vger.kernel.org
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/process.c

@@ -983,7 +983,7 @@ void restore_tm_state(struct pt_regs *regs)
 static inline void save_sprs(struct thread_struct *t)
 {
 #ifdef CONFIG_ALTIVEC
-	if (cpu_has_feature(cpu_has_feature(CPU_FTR_ALTIVEC)))
+	if (cpu_has_feature(CPU_FTR_ALTIVEC))
 		t->vrsave = mfspr(SPRN_VRSAVE);
 #endif
 #ifdef CONFIG_PPC_BOOK3S_64