Fix OV2740 build breakage by selecting REGMAP_I2C config:

ov2740.c:1011:23: error: variable has incomplete type 'struct regmap_config'
        struct regmap_config regmap_config = { };
                             ^
ov2740.c:1011:9: note: forward declaration of 'struct regmap_config'
        struct regmap_config regmap_config = { };
               ^
ov2740.c:1028:11: error: implicit declaration of function 'devm_regmap_init_i2c'
        regmap = devm_regmap_init_i2c(client, &regmap_config);
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>