s390/tape: remove redundant if statement

The unit check handler for 3480 / 3490 tapes used to print a different
warning message for erpa code 0x57 dependent on the device type.
The warning messages have been remove in a cleanup, the if statement
is a left over. Remove it.

Reported-by: Fraser Brown <mlfbrown@stanford.edu>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>