Mark registered_fb, num_registered_fb, fbcon_registered_fb, and
fbcon_num_registered_fb static to fix the following sparse
warnings:
drivers/video/fbdev/core/fbmem.c:51:16: sparse: warning: symbol 'registered_fb' was not declared. Should it be static?
drivers/video/fbdev/core/fbmem.c:52:5: sparse: warning: symbol 'num_registered_fb' was not declared. Should it be static?
drivers/video/fbdev/core/fbcon.c:105:16: sparse: warning: symbol 'fbcon_registered_fb' was not declared. Should it be static?
drivers/video/fbdev/core/fbcon.c:106:5: sparse: warning: symbol 'fbcon_num_registered_fb' was not declared. Should it be static?
No functional change intended.