i2c: acorn: fix i2c warning

The Acorn i2c driver (for RiscPC) triggers the "i2c adapter has no name"
warning in the I2C core driver, resulting in the RTC being inaccessible.
Fix this.

Fixes: 2236baa7 ("i2c: Sanity checks on adapter registration")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org