i2c: tegra: Fix PEC support for SMBUS block read

Update the msg->len value correctly for SMBUS block read. The discrepancy
went unnoticed as msg->len is used in SMBUS transfers only when a PEC
byte is added.

Fixes: d7583c8a ("i2c: tegra: Add SMBus block read function")
Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>