Revert previous break changes that return UC_ERR_ARG for non-existing registers

But print a warning instead

qemu/target/mips/unicorn.c

@@ -100,6 +100,7 @@ uc_err reg_read(void *_env, int mode, unsigned int regid, void *value,
         }
     }
 
+    CHECK_RET_DEPRECATE(ret, regid);
     return ret;
 }
 
@@ -149,6 +150,7 @@ uc_err reg_write(void *_env, int mode, unsigned int regid, const void *value,
         }
     }
 
+    CHECK_RET_DEPRECATE(ret, regid);
     return ret;
 }