MIPS: ensure MSA gets disabled during boot

The kernel relies upon MSA being disabled when a task begins running,
so that it can initialise or restore context in response to the
resulting MSA disabled exception. Previously the state of MSA following
boot was left as it was before the kernel ran, where MSA could
potentially have been enabled. Explicitly disable it during boot to
prevent any problems.

As a nice side effect the code reads a little better too.
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7306/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/kernel/cpu-probe.c

@@ -144,14 +144,13 @@ static inline int __cpu_has_fpu(void)
 
 static inline unsigned long cpu_get_msa_id(void)
 {
-	unsigned long status, conf5, msa_id;
+	unsigned long status, msa_id;
 
 	status = read_c0_status();
 	__enable_fpu(FPU_64BIT);
-	conf5 = read_c0_config5();
 	enable_msa();
 	msa_id = read_msa_ir();
-	write_c0_config5(conf5);
+	disable_msa();
 	write_c0_status(status);
 	return msa_id;
 }