i2c: stm32: fix usage of rise/fall device tree properties

These two device tree properties were not being applied.

Fixes: 1fd9eb68 ("i2c: stm32f7: move driver data of each instance in a privdata")
Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
Reviewed-by: Alain Volmat <alain.volmat@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Tested-by: Patrick Delaunay <patrick.delaunay@foss.st.com>