[SCSI] fix compile error on module_refcount

LD .tmp_vmlinux1
drivers/built-in.o(.text+0x8e1f9): In function `scsi_device_put':
drivers/scsi/scsi.c:887: undefined reference to `module_refcount'
make: *** [.tmp_vmlinux1] Error 1

There are only two users of module_refcount() outside of kernel/module.c
and the other one uses ifdef's similar to this.

Signed-Off-By: Daniel Walker <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/scsi.c

···
 {
 	struct module *module = sdev->host->hostt->module;
 
+#ifdef CONFIG_MODULE_UNLOAD
 	/* The module refcount will be zero if scsi_device_get()
 	 * was called from a module removal routine */
 	if (module && module_refcount(module) != 0)
 		module_put(module);
+#endif
 	put_device(&sdev->sdev_gendev);
 }
 EXPORT_SYMBOL(scsi_device_put);