of/flattree: forward declare struct device_node in of_fdt.h
of/flattree: forward declare struct device_node in of_fdt.h

This patch forward declares struct device_node to fix a compile error
when of_fdt.h is included, but of.h is not.  Alternately, including
linux/of.h could have been added to of_fdt.h, but that pulls in a lot
of unnecessary declarations when only working with the flattened
form.

Signed-off-by: Grant Likely <9069e6f5a2b566e2674a0ba1e2bf39c12c195fad@secretlab.ca>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas