FROMGIT: kbuild: make *.mod not depend on *.o

The dependency

    $(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o

... exists because *.mod files previously contained undefined symbols,
which are computed from *.o files when CONFIG_TRIM_UNUSED_KSYMS=y.

Now that the undefined symbols are put into separate *.usyms files,
there is no reason to make *.mod depend on *.o files.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Bug: 175420575
(cherry picked from commit 21b526ad634448369bbadc2f112ed2c716805e63
 https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git

 kbuild)
Change-Id: I7f0e7872ccb54467a33c951d0551fe49be9a36fd
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>