samples: cfb: text is not displayed due to display_blanking_off()

[KwonTae-young]

Describe the bug
samples/display/cfb uses display_blanking_off().

	}

	cfb_framebuffer_clear(dev, true);

	display_blanking_off(dev);

So text does not appear on the screen.
Instead of display_blanking_off(), use display_blanking_on() to display text.

To Reproduce
Board: frdm_k64f
SSD1306 Module: Adafruit PiOLED - 128x32 Monochrome OLED Add-on for Raspberry Pi

There is currently an I2C driver bug.(#8684)
The patch for #8684 (comment) needs to be applied.

mkdir samples/display/cfb/build
cd samples/display/cfb/build/
cmake -DBOARD=frdm_k64f ..
make -j8 flash

Expected behavior
I expected text to be displayed as below.

Impact
OLED is not displayed through samples/display/cfb.

Screenshots or console output
Corrected as shown below to display normally.

diff --git a/samples/display/cfb/src/main.c b/samples/display/cfb/src/main.c
index c314cbe419..a21b03ed01 100644
--- a/samples/display/cfb/src/main.c
+++ b/samples/display/cfb/src/main.c
@@ -50,7 +50,7 @@ void main(void)
 
        cfb_framebuffer_clear(dev, true);
 
-       display_blanking_off(dev);
+       display_blanking_on(dev);
 
        rows = cfb_get_display_parameter(dev, CFB_DISPLAY_ROWS);
        ppt = cfb_get_display_parameter(dev, CFB_DISPLAY_PPT);

It works even if it is modified as below.

diff --git a/samples/display/cfb/src/main.c b/samples/display/cfb/src/main.c
index c314cbe419..7411874e1b 100644
--- a/samples/display/cfb/src/main.c
+++ b/samples/display/cfb/src/main.c
@@ -50,8 +50,6 @@ void main(void)
 
        cfb_framebuffer_clear(dev, true);
 
-       display_blanking_off(dev);
-
        rows = cfb_get_display_parameter(dev, CFB_DISPLAY_ROWS);
        ppt = cfb_get_display_parameter(dev, CFB_DISPLAY_PPT);

Below is a running video.
Video: https://youtu.be/ovqmP0oC_5U

Environment:

• OS: Linux(Ubuntu 18.04)
• Toolchain: Zephyr SDK 0.9.5
• Commit SHA: 662b44e

Additional context
display_blanking_off(dev); has been added at eef1099

I'm sorry I do not have enough English.
Thank you.