staging: rtl8712: Remove duplicate #define for __attribute__ ((packed))

There is already a macro defined in linux/compiler.h.

Signed-off-by: Michael Fiedler <michael.fiedler@informatik.stud.uni-erlangen.de>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>