usb: storage: karma: remove useless variable

Remove the useless variable 'partial' storing the actual length
transferred. Nothing was done with it, so simply get rid of it
as usb_stor_bulk_transfer_buf can handle having NULL instead.

This also fixes the following sparse issues (-Wtypesign):
drivers/usb/storage/karma.c:122:51: warning: incorrect type in argument
5 (different signedness)
drivers/usb/storage/karma.c:122:51:    expected unsigned int *act_len
drivers/usb/storage/karma.c:122:51:    got int *<noident>
drivers/usb/storage/karma.c:127:52: warning: incorrect type in argument
5 (different signedness)
drivers/usb/storage/karma.c:127:52:    expected unsigned int *act_len
drivers/usb/storage/karma.c:127:52:    got int *<noident>

Signed-off-by: Pierre-Yves Kerbrat <pkerbrat@free.fr>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>