net: axienet: Fix check for partial TX checksum

Due to a typo, the code checked the RX checksum feature in the TX path.

Fixes: 8a3b7a25

 ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Link: https://lore.kernel.org/r/20231122004219.3504219-1-samuel.holland@sifive.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>