Remove redundant call to the sisfb_get_fix() before sis frambuffer is
registered.

This fixes a problem with uninitialized the fb_info->mm_lock mutex
introduced by the commit 537a1bf0 " fbdev: add mutex for fb_mmap
locking"
Signed-off-by: NKrzysztof Helt <krzysztof.h1@wp.pl>
Tested-by: NWu Zhangjin <wuzhangjin@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>