fbdev: Make fb_modesetting_disabled() static inline

Make fb_modesetting_disabled() a static-inline function when it is
defined in the header file. Avoid the linker error shown below.

 ld: drivers/video/fbdev/core/fbmon.o: in function `fb_modesetting_disabled':
 fbmon.c:(.text+0x1e4): multiple definition of `fb_modesetting_disabled'; drivers/video/fbdev/core/fbmem.o:fbmem.c:(.text+0x1bac): first defined here

A bug report is at [1].

Reported-by: Stephen Rothwell <[email protected]>
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Thomas Zimmermann <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
Fixes: 0ba2fa8 ("fbdev: Add support for the nomodeset kernel parameter")
Cc: Javier Martinez Canillas <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lore.kernel.org/dri-devel/[email protected]/T/#u # 1
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit a189b2e)

Author: Thomas Zimmermann

include/linux/fb.h

@@ -807,7 +807,7 @@ extern int fb_find_mode(struct fb_var_screeninfo *var,
 #if defined(CONFIG_VIDEO_NOMODESET)
 bool fb_modesetting_disabled(const char *drvname);
 #else
-bool fb_modesetting_disabled(const char *drvname)
+static inline bool fb_modesetting_disabled(const char *drvname)
 {
 	return false;
 }