nvmem: sunxi_sid: Read out SID for randomness without looping

Since the reg_read callbacks already support arbitrary, but 4-byte
aligned. offsets and lengths into the SID, there is no need for another
for loop just to use it to read 1 byte at a time.

Read out the whole SID block in one go.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>