frontend_ops before modifying

Fix: copy frontend_ops before modifying

Signed-off-by: Ye Jianjun (Joey) <joeyye@trident.com.cn>
Signed-off-by: Patrick Boettcher <pb@linuxtv.org>
Signed-off-by: Johannes Stezenbach <js@linuxtv.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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