usb: Remove __init from early_dbgp_init() prototype

Specifying these attributes in both the prototype and the function
definition is unnecessary and could cause confusion or bugs if they are
inconsistent.  As such, __init should only be specified at the function
definition.

Keith Owens suggested this as a janitorial task on LKML several years
ago:

  https://lkml.org/lkml/2006/1/14/305



Signed-off-by: Chris Rorvick <chris@rorvick.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>