firmware: use 'kernel_read()' to read firmware into kernel buffer

Fengguang correctly points out that the firmware reading should not use
vfs_read(), since the buffer is in kernel space.

The vfs_read() just happened to work for kernel threads, but sparse
warns about the incorrect address spaces, and it's definitely incorrect
and could fail for other users of the firmware loading.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/base/firmware_class.c

@@ -58,7 +58,6 @@ static noinline long fw_file_size(struct file *file)
 
 static bool fw_read_file_contents(struct file *file, struct firmware *fw)
 {
-	loff_t pos;
 	long size;
 	char *buf;
 
@@ -68,8 +67,7 @@ static bool fw_read_file_contents(struct file *file, struct firmware *fw)
 	buf = vmalloc(size);
 	if (!buf)
 		return false;
-	pos = 0;
-	if (vfs_read(file, buf, size, &pos) != size) {
+	if (kernel_read(file, 0, buf, size) != size) {
 		vfree(buf);
 		return false;
 	}