Fix typo in pico_rand breaking randomness when PICO_RAND_ENTROPY_SRC_BUS_PERF_COUNTER=1 (#1246)

src/rp2_common/pico_rand/rand.c

diff --git a/src/rp2_common/pico_rand/rand.c b/src/rp2_common/pico_rand/rand.c
index 0d1c6c5..e1cde58 100644
--- a/src/rp2_common/pico_rand/rand.c
+++ b/src/rp2_common/pico_rand/rand.c
@@ -272,7 +272,7 @@
     if (bus_counter_value == BUSCTRL_PERFCTR0_BITS) {
         bus_ctrl_hw->counter[bus_counter_idx].value = 0;
     }
-    local_rng_state.r[which] &= splitmix64(bus_counter_value);
+    local_rng_state.r[which] ^= splitmix64(bus_counter_value);
     which ^= 1;
 #endif