UBI: use vmalloc for large buffers

UBI allocates temporary buffers of PEB size, which may be 256KiB.
Use vmalloc instead of kmalloc for such big temporary buffers.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/misc.c b/drivers/mtd/ubi/misc.c
index 38d4e67..9e2338c 100644
--- a/drivers/mtd/ubi/misc.c
+++ b/drivers/mtd/ubi/misc.c
@@ -67,7 +67,7 @@
 	if (vol->vol_type != UBI_STATIC_VOLUME)
 		return 0;
 
-	buf = kmalloc(vol->usable_leb_size, GFP_KERNEL);
+	buf = vmalloc(vol->usable_leb_size);
 	if (!buf)
 		return -ENOMEM;
 
@@ -87,7 +87,7 @@
 		}
 	}
 
-	kfree(buf);
+	vfree(buf);
 	return err;
 }