AP_HAL: Change the return type of 'peekiovec'

Possible values are '0', '1' and '2' so uint8_t is a better fit. Also,
invert 'if' condition so it's clear that is returning 0, 1 or 2.

libraries/AP_HAL/utility/RingBuffer.cpp

@@ -96,7 +96,7 @@ bool ByteBuffer::advance(uint32_t n)
     return true;
 }
 
-int ByteBuffer::peekiovec(ByteBuffer::IoVec iovec[2], uint32_t len)
+uint8_t ByteBuffer::peekiovec(ByteBuffer::IoVec iovec[2], uint32_t len)
 {
     if (len > available()) {
         len = available();
@@ -113,14 +113,14 @@ int ByteBuffer::peekiovec(ByteBuffer::IoVec iovec[2], uint32_t len)
     iovec[0].data = const_cast<uint8_t *>(b);
     iovec[0].len = n;
 
-    if (len > n) {
-        iovec[1].data = buf;
-        iovec[1].len = len - n;
-
-        return 2;
+    if (len <= n) {
+        return 1;
     }
 
-    return 1;
+    iovec[1].data = buf;
+    iovec[1].len = len - n;
+
+    return 2;
 }
 
 /*

libraries/AP_HAL/utility/RingBuffer.h

@@ -74,13 +74,13 @@ public:
     uint32_t peekbytes(uint8_t *data, uint32_t len);
 
     // Similar to peekbytes(), but will fill out IoVec struct with
-    // both parts of the ring buffer if wraparound is happpening, or
+    // both parts of the ring buffer if wraparound is happening, or
     // just one part. Returns the number of parts written to.
     struct IoVec {
         uint8_t *data;
         uint32_t len;
     };
-    int peekiovec(IoVec vec[2], uint32_t len);
+    uint8_t peekiovec(IoVec vec[2], uint32_t len);
 
     // Reserve `len` bytes and fills out `vec` with both parts of the
     // ring buffer (if wraparound is happening), or just one contiguous