go/loader: Fix thinko in FindPackage hook signature

(*build.Context).Import has signature of

	(ctx, importPath, fromDir, mode)

not

	(ctx, fromDir, importPath, mode)

and the loader actually uses the first version.

The thinko was introduced in d6e83e53 (go/loader: changes for vendor
support; CL 18053) and was possible because importPath and fromDir both
have the same type string.

Fix it.

Change-Id: I52deaec6d141846b8a495835b121c1bdc2864215
Reviewed-on: https://go-review.googlesource.com/47343
Reviewed-by: Alan Donovan <adonovan@google.com>
1 file changed