ALSA: sound/atmel/ac97c.c: Add missing clock prepare

ALSA: sound/atmel/ac97c.c: Add missing clock prepare

Clocks must be prepared before enabling them. Do this in one step.
Replace clk_enable with clk_prepare_enable and clk_disable with
clk_disable_unprepare. This fixes the following warning:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at drivers/clk/clk.c:895 __clk_enable+0x24/0x9c()
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Tainted: G        W      3.18.0-rc7+ #245
[<c000dce8>] (unwind_backtrace) from [<c000bcf0>] (show_stack+0x10/0x14)
[<c000bcf0>] (show_stack) from [<c001664c>] (warn_slowpath_common+0x60/0x80)
[<c001664c>] (warn_slowpath_common) from [<c00166fc>] (warn_slowpath_null+0x18/0x20)
[<c00166fc>] (warn_slowpath_null) from [<c02fd7ac>] (__clk_enable+0x24/0x9c)
[<c02fd7ac>] (__clk_enable) from [<c02fdbb4>] (clk_enable+0x18/0x2c)
[<c02fdbb4>] (clk_enable) from [<c0322688>] (atmel_ac97c_probe+0x154/0x694)
[<c0322688>] (atmel_ac97c_probe) from [<c0235e08>] (platform_drv_probe+0x48/0x94)
[<c0235e08>] (platform_drv_probe) from [<c02345f8>] (driver_probe_device+0x138/0x350)
[<c02345f8>] (driver_probe_device) from [<c02348bc>] (__driver_attach+0x68/0x8c)
[<c02348bc>] (__driver_attach) from [<c0232bd0>] (bus_for_each_dev+0x70/0x84)
[<c0232bd0>] (bus_for_each_dev) from [<c0233cd8>] (bus_add_driver+0xfc/0x1f8)
[<c0233cd8>] (bus_add_driver) from [<c0234f0c>] (driver_register+0x9c/0xe0)
[<c0234f0c>] (driver_register) from [<c0008ac4>] (do_one_initcall+0x110/0x1c8)
[<c0008ac4>] (do_one_initcall) from [<c053cd58>] (kernel_init_freeable+0xf8/0x1b8)
[<c053cd58>] (kernel_init_freeable) from [<c03c0414>] (kernel_init+0x8/0xe4)
[<c03c0414>] (kernel_init) from [<c00096d0>] (ret_from_fork+0x14/0x24)
---[ end trace cb88537fdc8fa201 ]---
atmel_ac97c fffa0000.sound: AC'97 0 does not respond - RESET
atmel_ac97c fffa0000.sound: AC'97 0 access is not valid [0xffffffff], removing mixer.
------------[ cut here ]------------

Signed-off-by: Alexander Stein <alexanders83@web.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>