ja3: fix minor format string warning

ja3: fix minor format string warning

cppcheck:

src/util-ja3.c:197:28: warning: %d in format string (no. 1) requires 'int' but the argument type is 'unsigned int'. [invalidPrintfArgType_sint]
        (*buffer)->used += snprintf((*buffer)->data, (*buffer)->size, "%d",
                           ^
src/util-ja3.c:201:28: warning: %d in format string (no. 1) requires 'int' but the argument type is 'unsigned int'. [invalidPrintfArgType_sint]
        (*buffer)->used += snprintf((*buffer)->data + (*buffer)->used,
                           ^

Bug: #5291.