fbdev: fbcon: release buffer when fbcon_do_set_font() failed

In the Linux kernel, the following vulnerability has been resolved: fbdev: fbcon: release buffer when fbcon_do_set_font() failed syzbot is reporting memory leak at fbcon_do_set_font() [1], for commit a5a923038d70 ("fbdev: fbcon: Properly revert changes when vc_resize() failed") missed that the buffer might be newly allocated by fbcon_set_font().