drivers:net: Remove dma_alloc_coherent OOM messages

I believe these error messages are already logged
on allocation failure by warn_alloc_failed and so
get a dump_stack on OOM.

Remove the unnecessary additional error logging.

Around these deletions:

o Alignment neatening.
o Remove unnecessary casts of dma_alloc_coherent.
o Hoist assigns from ifs.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>