i2c: smbus: switch from loops to memcpy

When copying memory from one buffer to another, instead of open-coding
loops with byte-by-byte copies let's use memcpy() which might be a bit
faster and makes intent more clear.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>