fbmem: fix horribly incorrect placement of __maybe_unused

fbmem: fix horribly incorrect placement of __maybe_unused

Commit b9d79e4ca4ff ("fbmem: Mark proc_fb_seq_ops as __maybe_unused")
places the '__maybe_unused' in an entirely incorrect location between
the "struct" keyword and the structure name.

It's a wonder that gcc accepts that silently, but clang quite reasonably
warns about it:

    drivers/video/fbdev/core/fbmem.c:736:21: warning: attribute declaration must precede definition [-Wignored-attributes]
    static const struct __maybe_unused seq_operations proc_fb_seq_ops = {
                        ^

Fix it.

Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>