i2c: at91: fix clk_offset for sama5d2

In SAMA5D2 datasheet, TWIHS_CWGR register rescription mentions clock
offset of 3 cycles (compared to 4 in eg. SAMA5D3).

Cc: stable@vger.kernel.org # 5.2.x
[needs applying to i2c-at91.c instead for earlier kernels]
Fixes: 0ef6f321 ("i2c: at91: add support for new alternative command mode")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>