USB: serial drivers need to use larger bulk-in buffers

When a driver doesn't know how much data a device is going to send,
the buffer size should be at least as big as the endpoint's maxpacket
value.  The serial drivers don't follow this rule; many of them
request only 256-byte bulk-in buffers.  As a result, they suffer
overflow errors if a high-speed device wants to send a lot of data,
because high-speed bulk endpoints are required to have a maxpacket
size of 512.

This patch (as1450) fixes the problem by using the driver's
bulk_in_size value as a minimum, always allocating buffers no smaller
than the endpoint's maxpacket size.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Flynn Marquardt <flynn@flynnux.de>
CC: <stable@kernel.org> [after .39-rc1 is out]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>