#483 Fix SDAS incbin search path

[Michel Iwaniec]

This patch changes the search path for .incbin to be consistent with the search path for .include, so that they both behave consistently.

It is a one-line fix that just replaces the direct call to fopen in the incbin code section with search_path_fopen, as used in the include code section.

[Maarten Brock]

Applied in [r15124].
Thanks