BUILD: plock: remove dead code that causes a warning in gcc 11

As Ilya reported in issue #998, gcc 11 complains about misleading code
indentation which is in fact caused by dead assignments to zero after
a loop which stops on zero. Let's clean both of these.
diff --git a/include/import/plock.h b/include/import/plock.h
index 22244c5..058cc18 100644
--- a/include/import/plock.h
+++ b/include/import/plock.h
@@ -233,7 +233,6 @@
 				while (__pl_r)                                                 \
 					__pl_r = pl_deref_long(lock) -                         \
 						(PLOCK64_WL_1 | PLOCK64_SL_1 | PLOCK64_RL_1);  \
-					__pl_r = 0;                                            \
 			}                                                                      \
 		}                                                                              \
 		!__pl_r; /* return value */                                                    \
@@ -251,7 +250,6 @@
 				while (__pl_r)                                                 \
 					__pl_r = pl_deref_int(lock) -                          \
 						(PLOCK32_WL_1 | PLOCK32_SL_1 | PLOCK32_RL_1);  \
-					__pl_r = 0;                                            \
 			}                                                                      \
 		}                                                                              \
 		!__pl_r; /* return value */                                                    \