drivers/rtc/rtc-ds1307.c: fix BUG shown with lock debugging enabled

Add struct bin_attribute initialization to fix the following bug:

rtc-ds1307 3-0068: rtc core: registered ds1307 as rtc0
BUG: key cfb14fcc not in .data!
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WARNING: at kernel/lockdep.c:2986 sysfs_add_file_mode+0x84/0xdc()
Modules linked in:
[<c0018d94>] (unwind_backtrace+0x0/0xf8) from [<c0031f7c>] (warn_slowpath_common+0x4c/0x64)
[<c0031f7c>] (warn_slowpath_common+0x4c/0x64) from [<c0031fb0>] (warn_slowpath_null+0x1c/0x24)
[<c0031fb0>] (warn_slowpath_null+0x1c/0x24) from [<c012f7ac>] (sysfs_add_file_mode+0x84/0xdc)
[<c012f7ac>] (sysfs_add_file_mode+0x84/0xdc) from [<c04b11e4>] (ds1307_probe+0x5e4/0x6ac)
[<c04b11e4>] (ds1307_probe+0x5e4/0x6ac) from [<c036e600>] (i2c_device_probe+0xdc/0x108)
[<c036e600>] (i2c_device_probe+0xdc/0x108) from [<c02cdf84>] (driver_probe_device+0x90/0x210)
[<c02cdf84>] (driver_probe_device+0x90/0x210) from [<c02ce198>] (__driver_attach+0x94/0x98)
[<c02ce198>] (__driver_attach+0...