loongarch: Fixed dzamax

Initialize the registers to prevent sporadic errors.

kernel/loongarch64/camax_lasx.S

@@ -60,6 +60,7 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     PROLOGUE
     xvxor.v VM0, VM0, VM0
     xvxor.v res0, res0, res0
+    xvxor.v $xr20, $xr20, $xr20
     bge $r0, N, .L999
     bge $r0, INCX, .L999
     li.d TEMP, 1

kernel/loongarch64/camax_lsx.S

@@ -60,6 +60,7 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     PROLOGUE
     vxor.v VM0, VM0, VM0
     vxor.v res0, res0, res0
+    vxor.v $vr20, $vr20, $vr20
     bge $r0, N, .L999
     bge $r0, INCX, .L999
     li.d TEMP, 1