staging: r8712u: Remove unneeded local variable in _malloc in osdep_service.h header

The variable 'pbuf' is not needed.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>