staging: gpib: Fix faulty workaround for assignment in if

This was detected by Coverity.

Add the missing assignment in the else branch of the if

Reported-by: Kees Bakker <kees@ijzerbout.nl>
Fixes: fce79512a9 ("staging: gpib: Add LPVO DIY USB GPIB driver")
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20241204145713.11889-5-dpenkler@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/gpib/lpvo_usb_gpib/lpvo_usb_gpib.c

@@ -901,7 +901,7 @@ static int usb_gpib_read(gpib_board_t *board,
 
 		} else {
 			/* we are in the closing <DLE><ETX> sequence */
-
+			c = nc;
 			if (c == ETX) {
 				c = one_char(board, &b);
 				if (c == ACK) {