staging: rts5208: rtsx.c: Alloc sizeof struct

Satisfy checkpatch message:  Prefer kzalloc(sizeof(*dev->chip)...) over
kzalloc(sizeof(struct rtsx_chip)...)

Signed-off-by: Wayne Porter <wporter82@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>