rename GetFileSize to get_file_size for cygwin compilation
rename GetFileSize to get_file_size for cygwin compilation

boundarydevices/imx_usb_loader,pacificIT/imx_usb_loader,Adellica/imx_usb_loader,bwalle/imx_usb_loader,lucaceresoli/imx_usb_loader,vstehle/imx_usb_loader