Fix a typo in the free slave id search loop. Instead of I2C_CLIENT_PEC,
it should have been I2C_CLIENT_TEN. The slave id 1 can only handle 7-bit
addresses and thus is not eligible in case of 10-bit addresses.
As a matter of fact none of the slave id support I2C_CLIENT_PEC, overall
check is performed at the beginning of the stm32f7_i2c_reg_slave function.

Fixes: 60d609f3 ("i2c: i2c-stm32f7: Add slave support")
Signed-off-by: Alain Volmat <alain.volmat@st.com>
Reviewed-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>