net/ti davinci_mdio: don't hold a spin lock while calling pm_runtime

net/ti davinci_mdio: don't hold a spin lock while calling pm_runtime

was playing with suspend and run into this:

|BUG: sleeping function called from invalid context at drivers/base/power/runtime.c:891
|in_atomic(): 1, irqs_disabled(): 0, pid: 1963, name: bash
|6 locks held by bash/1963:
|CPU: 0 PID: 1963 Comm: bash Not tainted 3.10.0-rc4+ #50
|[<c0014fdc>] (unwind_backtrace+0x0/0xf8) from [<c0011da4>] (show_stack+0x10/0x14)
|[<c0011da4>] (show_stack+0x10/0x14) from [<c02e8680>] (__pm_runtime_idle+0xa4/0xac)
|[<c02e8680>] (__pm_runtime_idle+0xa4/0xac) from [<c0341158>] (davinci_mdio_suspend+0x6c/0x9c)
|[<c0341158>] (davinci_mdio_suspend+0x6c/0x9c) from [<c02e0628>] (platform_pm_suspend+0x2c/0x54)
|[<c02e0628>] (platform_pm_suspend+0x2c/0x54) from [<c02e52bc>] (dpm_run_callback.isra.3+0x2c/0x64)
|[<c02e52bc>] (dpm_run_callback.isra.3+0x2c/0x64) from [<c02e57e4>] (__device_suspend+0x100/0x22c)
|[<c02e57e4>] (__device_suspend+0x100/0x22c) from [<c02e67e8>] (dpm_suspend+0x68/0x230)
|[<c02e67e8>] (dpm_suspend+0x68/0x230) from [<c0072a20>] (suspend_devices_and_enter+0x68/0x350)
|[<c0072a20>] (suspend_devices_and_enter+0x68/0x350) from [<c0072f18>] (pm_suspend+0x210/0x24c)
|[<c0072f18>] (pm_suspend+0x210/0x24c) from [<c0071c74>] (state_store+0x6c/0xbc)
|[<c0071c74>] (state_store+0x6c/0xbc) from [<c02714dc>] (kobj_attr_store+0x14/0x20)
|[<c02714dc>] (kobj_attr_store+0x14/0x20) from [<c01341a0>] (sysfs_write_file+0x16c/0x19c)
|[<c01341a0>] (sysfs_write_file+0x16c/0x19c) from [<c00ddfe4>] (vfs_write+0xb4/0x190)
|[<c00ddfe4>] (vfs_write+0xb4/0x190) from [<c00de3a4>] (SyS_write+0x3c/0x70)
|[<c00de3a4>] (SyS_write+0x3c/0x70) from [<c000e2c0>] (ret_fast_syscall+0x0/0x48)

I don't see a reason why the pm_runtime call must be under the lock.
Further I don't understand why this is a spinlock and not mutex.

Cc: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>