USB: gadget: dummy-hcd: Fix errors in port-reset handling

USB: gadget: dummy-hcd: Fix errors in port-reset handling

Commit c318840fb2a4 ("USB: Gadget: dummy-hcd: Fix shift-out-of-bounds
bug") messed up the way dummy-hcd handles requests to turn on the
RESET port feature (I didn't notice that the original switch case
ended with a fallthrough).  The call to set_link_state() was
inadvertently removed, as was the code to set the USB_PORT_STAT_RESET
flag when the speed is USB2.

In addition, the original code never checked whether the port was
connected before handling the port-reset request.  There was a check
for the port being powered, but it was removed by that commit!  In
practice this doesn't matter much because the kernel doesn't try to
reset disconnected ports, but it's still bad form.

This patch fixes these problems by changing the fallthrough to break,
adding back in the missing set_link_state() call, setting the
port-reset status flag, adding a port-is-connected test, and removing
a redundant assignment statement.

Fixes: c318840fb2a4 ("USB: Gadget: dummy-hcd: Fix shift-out-of-bounds bug")
CC: <stable@vger.kernel.org>
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20210113194510.GA1290698@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>