pngcrush_1.6.4.bb : use BPN(fixes pngcrush-native install)

pngcrush_1.6.4.bb : use BPN(fixes pngcrush-native install)

The problem is that pngcrush-native fails during the installation
  because of this code in pngcrush_1.6.4.bb:
   install -m 755 ${PN} ${D}${bindir}
  that is in the do_install function.
  This code is inherited by pngcrush-native because
  pngcrush-native requires pngcrush_${PV}.bb,and PN becomes pngcrush-native
  instead of pngcrush and so it fails.

  Thanks hrw for learning me how to fix it easily(without copying
   the do_install function from pngcrush_1.6.4.bb into pngcrush-native)

  The effect of BPN on the 2 recipes was tested in bitbake -i

  Not changing PR because it doesn't change anything on
   pngcrush_1.6.4.bb's side,and on pngcrush-native's side it was
   just a compilation failure