usb: ftdi-elan: Fix if == else warnings in ftdi_elan_respond_engine

Fixes the following coccinelle warning:
./drivers/usb/misc/ftdi-elan.c:972:10-12: WARNING: possible condition with no effect (if == else)
./drivers/usb/misc/ftdi-elan.c:983:9-11: WARNING: possible condition with no effect (if == else)
./drivers/usb/misc/ftdi-elan.c:2052:11-13: WARNING: possible condition with no effect (if == else)

All these else/if branches just do the same thing actually as the last else branch,
So it can be merged into the last branch.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>