staging: r8188eu: rename _rtw_open_pktfile()

There is no need to prefix the function name of _rtw_open_pktfile()
with an underscore. Rename it to rtw_open_pktfile().

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220820181623.12497-10-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>