Fix warning from static analysis in floating-point test  (#178)

This makes one of the parameters in the floating point test const as recommended by cppcheck for general code hygiene.


* Fix warning from static analysis

const-qualify *half to silence the warning

Update declaration of decode_half

* Fix warning from static analysis
diff --git a/test/qcbor_encode_tests.c b/test/qcbor_encode_tests.c
index 6e569ca..5c59fe1 100644
--- a/test/qcbor_encode_tests.c
+++ b/test/qcbor_encode_tests.c
@@ -74,7 +74,7 @@
    size_t i;
    for(i = 0; i < U1.len; i++) {
       if(((uint8_t *)U1.ptr)[i] != ((uint8_t *)U2.ptr)[i]) {
-         printf("Position: %d  Actual: 0x%x   Expected: 0x%x\n",
+         printf("Position: %u  Actual: 0x%x   Expected: 0x%x\n",
                 (uint32_t)i,
                 ((uint8_t *)U1.ptr)[i],
                 ((uint8_t *)U2.ptr)[i]);