usb: class: dfu: fix USB descriptors in composite mode
usb: class: dfu: fix USB descriptors in composite mode

In composite mode the request handler buffer is common to all functions,
and its size is defined by CONFIG_USB_COMPOSITE_BUFFER_SIZE.

Given the device is enumerated as composite in runtime mode and
as legacy in download mode, we need to define wTransferSize as
the minimum of the two.

Signed-off-by: Aurelien Jarno <bceb368e7f2cb351af47298f32034f0587bbe4a6@aurel32.net>

explora26/zephyr,ldts/zephyr,Vudentz/zephyr,finikorg/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,finikorg/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,galak/zephyr,ldts/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,finikorg/zephyr,nashif/zephyr,ldts/zephyr,galak/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,explora26/zephyr,galak/zephyr