usb_master: Store maximum packet size for bulk endpoints

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
usb_master: Use endpoint size for bulk transfer size

Do not hardcode the packet size to 64 bytes, but instead use the value from
the endpoint descriptor.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>