net: moxa: fix endianness-related issues from 'sparse'

net: moxa: fix endianness-related issues from 'sparse'

Sparse checker found two endianness-related issues:

.../moxart_ether.c:34:15: warning: incorrect type in assignment (different base types)
.../moxart_ether.c:34:15:    expected unsigned int [usertype]
.../moxart_ether.c:34:15:    got restricted __le32 [usertype]

.../moxart_ether.c:39:16: warning: cast to restricted __le32

Fix them by using __le32 type instead of u32.

Signed-off-by: Sergei Antonov <saproj@gmail.com>
Link: https://lore.kernel.org/r/20220902125037.1480268-1-saproj@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>