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>

Makefile

@@ -852,10 +852,10 @@ export mod_strip_cmd
 mod_compress_cmd = true
 ifdef CONFIG_MODULE_COMPRESS
   ifdef CONFIG_MODULE_COMPRESS_GZIP
-    mod_compress_cmd = gzip -n
+    mod_compress_cmd = gzip -n -f
   endif # CONFIG_MODULE_COMPRESS_GZIP
   ifdef CONFIG_MODULE_COMPRESS_XZ
-    mod_compress_cmd = xz
+    mod_compress_cmd = xz -f
   endif # CONFIG_MODULE_COMPRESS_XZ
 endif # CONFIG_MODULE_COMPRESS
 export mod_compress_cmd