i2c: remove redundant condition

I2C_M_RD is defined as and guaranteed to be 1 and 'flag & I2C_M_RD' is
one or zero. No need for an additional condition to obtain the value.

Signed-off-by: Hsin-Yu.Chen <harry021633@gmail.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
[wsa: slightly updated commit message]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>