Fix of UPM driver for Freescale PowerPC processors

If Freescale LBC driver fails to initialise itself from device tree,
then internal structure is freed only but not NULL-fied.
As result functions fsl_lbc_find() after checking the structure is not NULL are
trying to access device registers.

Signed-off-by: Alexandre Rusev <arusev@dev.rtsoft.ru> 
--- linux-2.6.39.old/arch/powerpc/sysdev/fsl_lbc.c	2011-10-27 03:17:28.000000000 +0400
+++ linux-2.6.39/arch/powerpc/sysdev/fsl_lbc.c	2011-10-27 05:06:44.000000000 +0400
@@ -322,6 +322,7 @@ static int __devinit fsl_lbc_ctrl_probe(
 err:
 	iounmap(fsl_lbc_ctrl_dev->regs);
 	kfree(fsl_lbc_ctrl_dev);
+	fsl_lbc_ctrl_dev = NULL;
 	return ret;
 }