main: fixup log message to fixed type

By statically casting to a fixed-size type we can ensure the code
compiles the same for 64-bit and 32-bit environments (for the most
part w.r.t this).

Change-Id: If4989c7d3d0879e08be89dfa2a7846cf06dee883
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/main.cpp b/main.cpp
index ef6508b..4b8bc61 100644
--- a/main.cpp
+++ b/main.cpp
@@ -51,7 +51,8 @@
     // Verify it's at least as long as it needs to be for a subcommand.
     if ((*dataLen) < 1)
     {
-        fprintf(stderr, "*dataLen too small: %lu\n", (*dataLen));
+        fprintf(stderr, "*dataLen too small: %u\n",
+                static_cast<uint32_t>(*dataLen));
         return IPMI_CC_INVALID;
     }