i2c: designware: Optimize flag reading in i2c_dw_read()

i2c: designware: Optimize flag reading in i2c_dw_read()

Optimize the i2c_dw_read() function by reading the message flags only
once per message, rather than for every byte.

The message flags are accessed both in the outer loop and the inner loop,
so move the declaration of the local flags variable to the outer loop.

The message index is only modified by the outer loop, so reading the
flags in the inner loop was always getting the same value.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20251126-i2c-dw-v4-2-b0654598e7c5@bootlin.com