Only initialize mmap and draw helpers with macros; leave read/write
callbacks to driver implementations. Fixes the following warnings:

  CC [M]  drivers/video/fbdev/sm712fb.o
  sm712fb.c:1355:25: warning: initialized field overwritten [-Woverride-init]
  1355 |         .fb_fillrect  = cfb_fillrect,
       |                         ^~~~~~~~~~~~
  sm712fb.c:1355:25: note: (near initialization for 'smtcfb_ops.fb_fillrect')
  sm712fb.c:1356:25: warning: initialized field overwritten [-Woverride-init]
  1356 |         .fb_imageblit = cfb_imageblit,
       |                         ^~~~~~~~~~~~~
  sm712fb.c:1356:25: note: (near initialization for 'smtcfb_ops.fb_imageblit')
  sm712fb.c:1357:25: warning: initialized field overwritten [-Woverride-init]
  1357 |         .fb_copyarea  = cfb_copyarea,
       |                         ^~~~~~~~~~~~
  sm712fb.c:1357:25: note: (near initialization for 'smtcfb_ops.fb_copyarea')
  sm712fb.c:1358:25: warning: initialized field overwritten [-Woverride-init]
  1358 |         .fb_read      = smtcfb_read,
       |                         ^~~~~~~~~~~
  sm712fb.c:1358:25: note: (near initialization for 'smtcfb_ops.fb_read')
  sm712fb.c:1359:25: warning: initialized field overwritten [-Woverride-init]
  1359 |         .fb_write     = smtcfb_write,
       |                         ^~~~~~~~~~~~
  sm712fb.c:1359:25: note: (near initialization for 'smtcfb_ops.fb_write')
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 586132cf ("fbdev/sm712fb: Initialize fb_ops to fbdev I/O-memory helpers")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-fbdev@vger.kernel.org
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231127131655.4020-3-tzimmermann@suse.de