nvmem: meson-mx-efuse: allow reading data smaller than word_size

Some Amlogic boards store the Ethernet MAC address inside the eFuse. The
Ethernet MAC address uses 6 bytes. The existing logic in
meson_mx_efuse_read() would write beyond the end of the data buffer when
trying to read data with a size that is not aligned to word_size (4
bytes on Meson8, Meson8b and Meson8m2).

Calculate the remaining data to copy inside meson_mx_efuse_read() so
reading 6 bytes doesn't write beyond the end of the data buffer.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20190818093345.29647-5-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/meson-mx-efuse.c

@@ -155,7 +155,8 @@ static int meson_mx_efuse_read(void *context, unsigned int offset,
 		if (err)
 			break;
 
-		memcpy(buf + i, &tmp, efuse->config.word_size);
+		memcpy(buf + i, &tmp,
+		       min_t(size_t, bytes - i, efuse->config.word_size));
 	}
 
 	meson_mx_efuse_mask_bits(efuse, MESON_MX_EFUSE_CNTL1,