staging: rtl8188eu: remove _rtl88e_fill_dummy

The _rtl88e_fill_dummy function replaced by memset in rtl88eu_download_fw.

More appropriate names are used for pfwdata and fwsize variables
(download_data and download_size respectively).

Also u32 replaced by size_t for download_size variable.

Signed-off-by: Ivan Safonov <insafonov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>