staging: rts5208: Add a check for ms_read_extra_data

In ms_copy_page, the function ms_read_extra_data may fail for many
reasons. The fix adds a check similar to other invocation to return
error upstream.

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>