staging: rtl8712: usb_halinit.c: Remove p from variable names

Remove leading 'p' from the names of the following pointer variables:
    - padapter
    - precvbuf
    - pintfhdl
    - pregistrypriv
    - precvpriv.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>