firmware: hardcode the debug message for -ENOENT

When no file /path was found, the error code of -ENOENT
enumerated in errno-base.h, is returned. Stating clearly that
the file was not found is much more useful for debugging, So
let's be explicit about that.

Signed-off-by: John Zhao <yuankuiz@codeaurora.org>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>