phy: phy-brcm-usb-init: fix use of integer as pointer

The xhci_ec_base variable is a pointer, so don't compare
it with an integer.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>