target-mips: fix ASID synchronisation for MIPS MT

When syncing the task ASID with EntryHi, correctly or the value instead
of assigning it.
Reported-by: N"Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Cc: Leon Alrae <leon.alrae@imgtec.com>
Reviewed-by: NLeon Alrae <leon.alrae@imgtec.com>
Signed-off-by: NLeon Alrae <leon.alrae@imgtec.com>

target-mips/op_helper.c

@@ -661,7 +661,7 @@ static void sync_c0_tcstatus(CPUMIPSState *cpu, int tc,
 
     /* Sync the TASID with EntryHi.  */
     cpu->CP0_EntryHi &= ~0xff;
-    cpu->CP0_EntryHi = tasid;
+    cpu->CP0_EntryHi |= tasid;
 
     compute_hflags(cpu);
 }