net: mvmdio: rename base register cookie from smireg to regs

This patch renames the base register cookie in the mvmdio drive from
"smireg" to "regs" since a subsequent patch is going to use an ioremap()
cookie whose size is larger than a single register of 4 bytes. No
functionnal code change introduced.

Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>