cfg80211: always rewrite generated files from scratch

Currently the certs C code generation appends to the generated files,
which is most likely a leftover from commit 715a12334764 ("wireless:
don't write C files on failures"). This causes duplicate code in the
generated files if the certificates have their timestamps modified
between builds and thereby trigger the generation rules.

Fixes: 715a12334764 ("wireless: don't write C files on failures")
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/Makefile

@@ -43,7 +43,7 @@ $(obj)/shipped-certs.c: $(wildcard $(srctree)/$(src)/certs/*.x509)
 	      echo "$$allf"; \
 	      echo '};'; \
 	      echo 'unsigned int shipped_regdb_certs_len = sizeof(shipped_regdb_certs);'; \
-	  ) >> $@)
+	  ) > $@)
 
 $(obj)/extra-certs.c: $(CONFIG_CFG80211_EXTRA_REGDB_KEYDIR:"%"=%) \
 		      $(wildcard $(CONFIG_CFG80211_EXTRA_REGDB_KEYDIR:"%"=%)/*.x509)
@@ -66,4 +66,4 @@ $(obj)/extra-certs.c: $(CONFIG_CFG80211_EXTRA_REGDB_KEYDIR:"%"=%) \
 	      echo "$$allf"; \
 	      echo '};'; \
 	      echo 'unsigned int extra_regdb_certs_len = sizeof(extra_regdb_certs);'; \
-	  ) >> $@)
+	  ) > $@)