ftdi: Fix overflow of pulse/space values.
ftdi: Fix overflow of pulse/space values.

Values >= 8192 (2^13) were overflowing.

Tested with Humax DTR-T1000 (whose protocol uses a header pulse of
~9000) and the FTDI USB IR blaster from
http://www.irblaster.info/usb_blaster.html

stb-tester/lirc,stb-tester/lirc,stb-tester/lirc,stb-tester/lirc,stb-tester/lirc,stb-tester/lirc