MAINTAINERS: repair file entry in MEDIA DRIVERS FOR STM32 - CSI

Commit dcb0f4c1 ("media: stm32: csi: addition of the STM32 CSI driver")
adds a new driver at drivers/media/platform/st/stm32/stm32-csi.c, but
creates a new MAINTAINERS section MEDIA DRIVERS FOR STM32 - CSI with a file
entry pointing to drivers/media/platform/stm32/stm32-csi.c. Note that the
file entry is missing the ‘st’ directory in its path.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains about a
broken reference. Repair this file entry in MEDIA DRIVERS FOR STM32 - CSI.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Reviewed-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>