The system_fwrite function writes a specified number of bytes from a specified buffer into a specified file.
Before system_fwrite can be used, you must open the file using any of the system_fopen functions except system_fopenRO.
int system_fwrite(SYS_FILE fd, char *buf, int sz);
Returns IO_OKAY if the write succeeded, or IO_ERROR if the write failed.
SYS_FILE fd is the platform-independent file descriptor.
char *buf is the buffer containing the bytes to be written.
int sz is the number of bytes to write to the file.