greybus: fix some error codes

Change the message result values used in two cases.

First, use -EMSGSIZE rather than -E2BIG to represent a message
that is larger than the buffer intended to hold it.  That is
the proper code for this situation.

Second, use -ECANCELED rather than -EINTR for an operation that
has been canceled.  The definition of that error is literally
"Operation Canceled" so it seems like the right thing to do.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>