[S390] cio: change confusing message in cmf.

cmf currently prints a message that more than 4096 channels are not
allowed in basic mode - however, this can only be enforced if cmf was
a module (which is no longer possible). It makes much more sense to
not check the specified number of channels and just print a message if
the block for basic mode could not be allocated (which may happen for
any number of specified channels).

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>