i2c: nforce2: fix coding style issues

avoid these checkpatch.pl issues :
- ERROR: "foo * bar" should be "foo *bar"
- ERROR: switch and case should be at the same indent
- ERROR: "(foo*)" should be "(foo *)"
- ERROR: do not use assignment in if condition
- ERROR: space required before the open parenthesis '('
- WARNING: suspect code indent for conditional statements
- WARNING: quoted string split across lines
- WARNING: space prohibited between function name and open parenthesis '('
- WARNING: line over 80 characters
also add spaces around some "+", "=", "*"

Signed-off-by: Laurent Navet <laurent.navet@gmail.com>
Reviewed-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>