staging: sm750fb: Remove typedef struct _dvi_ctrl_device_t

This patch removes typedef from struct and renames it from
"_dvi_ctrl_device_t" to "dvi_ctrl_device" as per kernel coding
standards.

Issue found by checpatch.pl

Signed-off-by: Mihaela Muraru <mihaela.muraru21@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>