USB: g_printer.h does not need to be "unifdef"ed.

Since the header file g_printer.h doesn't depend on __KERNEL__,
there's no need to unifdef it in the Kbuild file.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>