dfu: handle short frame result of UPLOAD in state_dfu_idle

dfu: handle short frame result of UPLOAD in state_dfu_idle

In DFU v1.1 specification [1] the DFU_UPLOAD (Short Frame)
is handled only in dfuUPLOADIDLE state:

- Figure A.1 Interface state transition diagram

- the state description in chapter A.2

A.2.3 State 2 dfuIDLE
  on Receipt of the DFU_UPLOAD request,and bitCanUpload = 1
  the Next State is dfuUPLOADIDLE

A.2.10 State 9 dfuUPLOAD-IDLE
  When the length of the data transferred by the device in response
  to a DFU_UPLOAD request is less than wLength. (Short frame)
  the Next State is dfuIDLE

In current code, when an UPLOAD is completely performed after the first
request (for example with wLength=200 and data read = 9), the DFU state
stay at dfuUPLOADIDLE until receiving a DFU_UPLOAD or a DFU_ABORT request
even it is unnecessary as the previous DFU_UPLOAD request already reached
the EOF.

This patch proposes to finish the DFU uploading (don't go to dfuUPLOADIDLE)
and completes the control-read operation (go to DFU_STATE_dfuIDLE) when
the first UPLOAD response has a short frame as an end of file (EOF)
indicator even if it is not explicitly allowed in the DFU specification
but this seems logical.

[1] https://www.usb.org/sites/default/files/DFU_1.1.pdf

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>