Rework the make rule for patched *.c files.

Rework the make rule for patched *.c files.
Previously ${SRCS} contained the file name with and without
the directory part(hardware/hwsleep.c vs hwsleep.c), and
the object files from the latter are trimmed off of ${OBJS}.
This resulted in compiling both patched and unpatched version
and the object files get created under ${.OBJDIR}.
Also make a patched *.c file depend on the patch, so as the
*.c file is re-generated when the patch is updated.