lib/rand: cleanup __fill_random_buffer()

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/lib/rand.c b/lib/rand.c
index 32aec20..185b679 100644
--- a/lib/rand.c
+++ b/lib/rand.c
@@ -72,23 +72,23 @@
 	void *ptr = buf;
 
 	while (len) {
+		int this_len;
+
 		if (len >= sizeof(int64_t)) {
 			*((int64_t *) ptr) = seed;
-			ptr += sizeof(int64_t);
-			len -= sizeof(int64_t);
+			this_len = sizeof(int64_t);
 		} else if (len >= sizeof(int32_t)) {
 			*((int32_t *) ptr) = seed;
-			ptr += sizeof(int32_t);
-			len -= sizeof(int32_t);
+			this_len = sizeof(int32_t);
 		} else if (len >= sizeof(int16_t)) {
 			*((int16_t *) ptr) = seed;
-			ptr += sizeof(int16_t);
-			len -= sizeof(int16_t);
+			this_len = sizeof(int16_t);
 		} else {
 			*((int8_t *) ptr) = seed;
-			ptr += sizeof(int8_t);
-			len -= sizeof(int8_t);
+			this_len = sizeof(int8_t);
 		}
+		ptr += this_len;
+		len -= this_len;
 		seed *= GOLDEN_RATIO_PRIME;
 		seed >>= 3;
 	}