[mips][cleanup] Eliminate non-const reference parameters

Fix build errors introduced by

commit af063685

Change-Id: I467ea39f020d07bed00875f69152191b94029dd1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1794327
Auto-Submit: Mu Tao <pamilty@gmail.com>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63633}

src/codegen/mips/assembler-mips.cc

@@ -2969,7 +2969,7 @@ MSA_BRANCH_LIST(MSA_BRANCH)
 #define MSA_LD_ST(name, opcode)                                  \
   void Assembler::name(MSARegister wd, const MemOperand& rs) {   \
     MemOperand source = rs;                                      \
-    AdjustBaseAndOffset(source);                                 \
+    AdjustBaseAndOffset(&source);                                 \
     if (is_int10(source.offset())) {                             \
       GenInstrMsaMI10(opcode, source.offset(), source.rm(), wd); \
     } else {                                                     \

src/codegen/mips64/assembler-mips64.cc

@@ -3169,7 +3169,7 @@ MSA_BRANCH_LIST(MSA_BRANCH)
 #define MSA_LD_ST(name, opcode)                                  \
   void Assembler::name(MSARegister wd, const MemOperand& rs) {   \
     MemOperand source = rs;                                      \
-    AdjustBaseAndOffset(source);                                 \
+    AdjustBaseAndOffset(&source);                                 \
     if (is_int10(source.offset())) {                             \
       GenInstrMsaMI10(opcode, source.offset(), source.rm(), wd); \
     } else {                                                     \