fb: cfb: remove unnecessary NULL check and NULL assignment

Since the `fb` pointer is always assigned to `char_fb`, there is no need
for a `NULL` check. Additionally, removed setting `fb->buf` to `NULL` in
`cfb_framebuffer_init` as it will be overwritten by subsequent operations.

Signed-off-by: Pisit Sawangvonganan <[email protected]>

Author: ndrs-pst

subsys/fb/cfb.c

@@ -436,7 +436,7 @@ int cfb_framebuffer_clear(const struct device *dev, bool clear_display)
 {
 	const struct char_framebuffer *fb = &char_fb;
 
-	if (!fb || !fb->buf) {
+	if (!fb->buf) {
 		return -ENODEV;
 	}
 
@@ -465,7 +465,7 @@ int cfb_framebuffer_finalize(const struct device *dev)
 	struct display_buffer_descriptor desc;
 	int err;
 
-	if (!fb || !fb->buf) {
+	if (!fb->buf) {
 		return -ENODEV;
 	}
 
@@ -574,7 +574,6 @@ int cfb_framebuffer_init(const struct device *dev)
 	fb->ppt = 8U;
 	fb->pixel_format = cfg.current_pixel_format;
 	fb->screen_info = cfg.screen_info;
-	fb->buf = NULL;
 	fb->kerning = 0;
 	fb->inverted = false;