net: mhi_net: Update the transmit handler prototype

Update the function prototype of mhi_ndo_xmit to match
ndo_start_xmit. This otherwise leads to run time failures when
CFI is enabled in kernel.

Fixes: 3ffec6a1 ("net: Add mhi-net driver")
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>