firmware: make fw->data const

In preparation for supporting firmware files linked into the static
kernel, make fw->data const to ensure that users aren't modifying it (so
that we can pass a pointer to the original in-kernel copy, rather than
having to copy it).

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 9fd4a85..264b3a2 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -257,7 +257,7 @@
 	if (retval)
 		goto out;
 
-	memcpy(fw->data + offset, buffer, count);
+	memcpy((u8 *)fw->data + offset, buffer, count);
 
 	fw->size = max_t(size_t, offset + count, fw->size);
 	retval = count;