8294012: RISC-V: get/put_native_u8 missing the case when address&7 is 6

Reviewed-by: fyang, gcao
Backport-of: 09af637a9be106a0a6b82b3638ae004d9248fc78

Author: DingliZhang

src/hotspot/cpu/riscv/bytes_riscv.hpp

@@ -73,6 +73,7 @@ class Bytes: AllStatic {
                ((u8)(((u4*)p)[0]));
 
       case 2:
+      case 6:
         return ((u8)(((u2*)p)[3]) << 48) |
                ((u8)(((u2*)p)[2]) << 32) |
                ((u8)(((u2*)p)[1]) << 16) |
@@ -131,6 +132,7 @@ class Bytes: AllStatic {
         break;
 
       case 2:
+      case 6:
         ((u2*)p)[3] = x >> 48;
         ((u2*)p)[2] = x >> 32;
         ((u2*)p)[1] = x >> 16;