usb: host: ehci-platform: Update brcm, xgs-iproc-ehci workaround

The original workaround was added prior to commit e4788edc

 ("USB:
EHCI: Add alias for Broadcom INSNREG"). Now that brcm_insnreg exists in
struct ehci_regs we can use that instead of having a local definition.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Link: https://lore.kernel.org/r/20220215000813.1779032-1-chris.packham@alliedtelesis.co.nz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>