Makefile: Force gzip and xz on module install

Makefile: Force gzip and xz on module install

Running `make modules_install` ordinarily will overwrite existing
modules. This is the desired behavior, and is how pretty much every
other `make install` target works.

However, if CONFIG_MODULE_COMPRESS is enabled, modules are passed
through gzip and xz which then do the file writing. Both gzip and xz
will error out if the file already exists, unless -f is passed.

This patch adds -f so that the behavior is uniform.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Michal Marek <mmarek@suse.com>