staging: rts5208: rtsx.c: Fix invalid use of sizeof in rtsx_probe()

sizeof() when applied to a pointer typed expression gives the
size of the pointer, not that of the pointed data.

Fixes: 2eb9d8cb ("staging: rts5208: rtsx.c: Alloc sizeof struct")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>