video: fbdev: sm712fb.c: using __func__ macro for pr_debug

Inside function sm7xx_vga_setup()

Using a generic function macro for debug information display

Signed-off-by: Lynn Lei <lynnl.wit@gmail.com>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>