backports: add replace_fops()

This is needed by drivers/media/dvb-core/dvbdev.c and was added in:
commit e84f9e57b90ca89664d733a7cef19aa7ccd832f3
Author: Al Viro <viro@zeniv.linux.org.uk>
Date:   Sun Sep 22 14:17:15 2013 -0400

    consolidate the reassignments of ->f_op in ->open() instances

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
backports: refresh on next-20131113

== ckmake-report.log ==

1   2.6.25              [  OK  ]
2   2.6.26              [  OK  ]
3   2.6.27              [  OK  ]
4   2.6.28              [  OK  ]
5   2.6.29              [  OK  ]
6   2.6.30              [  OK  ]
7   2.6.31              [  OK  ]
8   2.6.32              [  OK  ]
9   2.6.33              [  OK  ]
10  2.6.34              [  OK  ]
11  2.6.35              [  OK  ]
12  2.6.36              [  OK  ]
13  2.6.37              [  OK  ]
14  2.6.38              [  OK  ]
15  2.6.39              [  OK  ]
16  3.0.101             [  OK  ]
17  3.1.10              [  OK  ]
18  3.10.17             [  OK  ]
19  3.11.6              [  OK  ]
20  3.12-rc7            [  OK  ]
21  3.2.52              [  OK  ]
22  3.3.8               [  OK  ]
23  3.4.67              [  OK  ]
24  3.5.7               [  OK  ]
25  3.6.11              [  OK  ]
26  3.7.10              [  OK  ]
27  3.8.13              [  OK  ]
28  3.9.11              [  OK  ]

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>