This patch fixes compilation warnings related to ssize_t when
dvblast is compiled on 64 bit machine. The fixed warnings are:

comm.c: In function "comm_Read":
comm.c:86:18: warning: format "%d" expects type "int", but argument 3 has type "ssize_t"
comm.c:168:14: warning: format "%d" expects type "int", but argument 5 has type "ssize_t"

dvblastctl.c: In function "main":
dvblastctl.c:248:18: warning: format "%d" expects type "int", but argument 3 has type "ssize_t"