[media] gspca - main: Add endpoint direction test in alt_xfer

This patch fixes a bug in gspca, more precisely in alt_xfer().

This function looks for an input transfer endpoint in an alternate setting.
By default it returns the first endpoint corresponding to the transfer type
indicated in parameter.
But with some USB devices, the first endpoint corresponding to the transfer
type is not always an INPUT endpoint but an OUTPUT one.

This patch adds the endpoint direction test to be sure to return an INPUT endpoint

Signed-off-by: Patrice CHOTARD <patricechotard@free.fr>
Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>