test: Fix LFSR period in comments

Verified using a Python implementation.

Co-authored-by: Daira Hopwood <daira@jacaranda.org>

src/bench/lockedpool.cpp

@@ -35,7 +35,7 @@ static void LockedPool(benchmark::State& state)
             bool lsb = s & 1;
             s >>= 1;
             if (lsb)
-                s ^= 0xf00f00f0; // LFSR period 0xf7ffffe0
+                s ^= 0xf00f00f0; // LFSR period 0xf7ffffe1
         }
     }
     for (void *ptr: addr)

src/test/allocator_tests.cpp

@@ -116,7 +116,7 @@ BOOST_AUTO_TEST_CASE(arena_tests)
         bool lsb = s & 1;
         s >>= 1;
         if (lsb)
-            s ^= 0xf00f00f0; // LFSR period 0xf7ffffe0
+            s ^= 0xf00f00f0; // LFSR period 0xf7ffffe1
     }
     for (void *ptr: addr)
         b.free(ptr);