i2c: Fix sparse warnings for I2C_BOARD_INFO()

Since the first argument to I2C_BOARD_INFO() must be a string constant,
there is no need to parenthesise it, and adding parentheses results in
an invalid initialiser for char[].  gcc obviously accepts this syntax as
an extension, but sparse complains, e.g.:

drivers/net/sfc/boards.c:173:2: warning: array initialized from parenthesized string constant

Therefore, remove the parentheses.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>