staging: rtl8192u: r8192U_core: clean C99 // comments

Replace C99 // comments by /* comments */ to follow the
kernel code style. Remove some unuseful comments.

Signed-off-by: Raphaël Beamonte <raphael.beamonte@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>