Update hp3900_rts8822.c

After increase the timeout from 10 to 60 seconds, the hp3970 can scan black and white 35mm films using the parameters Gray, 16 bit and 2400 dpi. More information in https://gitlab.com/sane-project/backends/issues/77

backend/hp3900_rts8822.c

@@ -7786,7 +7786,7 @@ Scan_Read_BufferA (struct st_device *dev, SANE_Int buffer_size, SANE_Int arg2,
 		      opStatus = Reading_Wait (dev, rd->Channels_per_dot,
 					       rd->Channel_size,
 					       iAmount,
-					       &rd->Bytes_Available, 10, sc);
+					       &rd->Bytes_Available, 60, sc);
 
 		      /* If something fails, perhaps we can read some bytes... */
 		      if (opStatus != OK)