i2c: i2c-stm32f7: fix no check on returned setup

i2c: i2c-stm32f7: fix no check on returned setup

BugLink: http://bugs.launchpad.net/bugs/1762370
commit 771b7bf05339081019d22452ebcab6929372e13e upstream.

Before assigning returned setup structure check if not null

Fixes: 463a9215f3ca7600b5ff ("i2c: stm32f7: fix setup structure")
Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>