drivers: eth_sam_gmac: remove possible null pointer dereference

Fix eth_tx function which was dereferencing a pointer before
checking that it is not null.

Tested on Atmel SMART SAM E70 Xplained board

Change-Id: Idae4cf9d9a80f6ee9f74a94dd1debe7511c5fab4
Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>
1 file changed