misc: rtsx: Fix impossible condition

A u8 can only go up to 255, condition n > 396 is
impossible, so change u8 to u16.

Signed-off-by: Rui Feng <rui_feng@realsil.com.cn>
Link: https://lore.kernel.org/r/1574214006-13540-1-git-send-email-rui_feng@realsil.com.cn


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>