EDAC, i82975x: Add ioremap_nocache() error handling

If ioremap_nocache() fails, it will return NULL. Which will then cause a
NULL-pointer dereference. Handle the returned value properly.

Signed-off-by: Arvind Yadav <[e-mail]>
Cc: "Arvind R." <[e-mail]>
Cc: linux-edac <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
[ Boris: massage commit message and improve error message. ]
Signed-off-by: Borislav Petkov <[e-mail]>

drivers/edac/i82975x_edac.c

···
 	}
 	mchbar &= 0xffffc000;	/* bits 31:14 used for 16K window */
 	mch_window = ioremap_nocache(mchbar, 0x1000);
+	if (!mch_window) {
+		edac_dbg(3, "error ioremapping MCHBAR!\n");
+		goto fail0;
+	}
 
 #ifdef i82975x_DEBUG_IOMEM
 	i82975x_printk(KERN_INFO, "MCHBAR real = %0x, remapped = %p\n",