random: correct spelling of "overwrites"

It was missing an 'r'.

Fixes: 186873c5 ("random: use simpler fast key erasure flow on per-cpu keys")
Signed-off-by: NJason A. Donenfeld <Jason@zx2c4.com>

drivers/char/random.c

@@ -229,7 +229,7 @@ static void crng_reseed(void)
 
 /*
  * This generates a ChaCha block using the provided key, and then
- * immediately overwites that key with half the block. It returns
+ * immediately overwrites that key with half the block. It returns
  * the resultant ChaCha state to the user, along with the second
  * half of the block containing 32 bytes of random data that may
  * be used; random_data_len may not be greater than 32.