i2c: mv64xxx: Apply errata delay only in standard mode

The errata FE-8471889 description has been updated. There is still a
timing violation for repeated start. But the errata now states that it
was only the case for the Standard mode (100 kHz), in Fast mode (400 kHz)
there is no issue.

This patch limit the errata fix to the Standard mode.

It has been tesed successfully on the clearfog (Aramda 388 based board).

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>