i2c: i801: Use PCI bus rescan mutex to protect P2SB access

As pointed out by Andy in [0] using a local mutex here isn't strictly
wrong but not sufficient. We should hold the PCI rescan lock for P2SB
operations.

[0] https://www.spinics.net/lists/linux-i2c/msg52717.html



Fixes: 1a987c69 ("i2c: i801: make p2sb_spinlock a mutex")
Reported-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>