usb: musb: omap2430: remove unused define

get_cpu_rev() is unused in this driver. It is probably legacy
code. So remove it.

Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>