drivers: i2c: Fix TOCTOU while transferring I2C messages

All the mesages are checked with _SYSCALL_MEMORY() prior to calling the
actual implementation function.  However, a race condition might happen
between the check and the call to _impl_i2c_transfer() itself.

Copy the msgs vector to a locally allocated array and pass it to the
transfer implementation.

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>