Fix error when build with clang 3.0

Fix error when build with clang 3.0

dumpcap.c:3981:88: error: implicit conversion loses integer precision: 'const __suseconds_t'
      (aka 'const long') to 'guint32' (aka 'unsigned int') [-Werror,-Wshorten-64-to-32]
                                                             phdr->ts.tv_sec, phdr->ts.tv_usec,
                                                                              ~~~~~~~~~^~~~~~~
dumpcap.c:3989:73: error: implicit conversion loses integer precision: 'const __suseconds_t'
      (aka 'const long') to 'guint32' (aka 'unsigned int') [-Werror,-Wshorten-64-to-32]
                                              phdr->ts.tv_sec, phdr->ts.tv_usec,
                                                               ~~~~~~~~~^~~~~~~

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@51250 f5534014-38df-0310-8fa8-9805f1628bb7