docs: i2c: summary: start sentences consistently.

Change the first paragraphs to contain only one space after the end of
the previous sentence like in the rest of the document.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>