net: davinci_emac: Round up top tx buffer boundaries for dcache ops

net: davinci_emac: Round up top tx buffer boundaries for dcache ops

check_cache_range() warns that the top boundaries are not properly
aligned when flushing or invalidating the buffers and make these
operations fail.

This gets rid of the remaining warnings:
CACHE: Misaligned operation at range

Signed-off-by: Karl Beldan <karl.beldan+oss@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>