net: Armada100: Fix compilation warnings

This patch fix compilation warnings for Armada100 FEC driver

Ref:
warning: dereferencing type-punned pointer will break
strict-aliasing rules

Signed-off-by: Ajay Bhargav <ajay.bhargav@einfochips.com>
Acked-by: Anatolij Gustschin <agust@denx.de>