net: ag71xx: Add missing check after DMA map

[ Upstream commit 96a1e15e ]

The DMA map functions can fail and should be tested for errors.

Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250716095733.37452-3-fourier.thomas@gmail.com


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