Staging: altpciechdma: Null deref in altpciechdma.c remove()

If dev is NULL it prints an error message.  The error message dereferences
dev.

Compile tested only.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Cc: Leon Woestenberg <leon.woestenberg@axon.tv>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>