platform/mellanox: Rename i2c bus to nr

Use Linux convention of nr instead of bus for i2c adapter number.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
[dvhart: refactored commit into smaller functional changes]
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>