scsi: make the LUN a parameter of scsi_detect_dev()

This is a cosmetic change. target and LUN have kind of the same role in
this function. One of them was passed as a parameter and the other was
embedded in a structure. For consistency, pass both of them as parameters.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>