drm: fb-helper: Convert logging to drm_* functions.

Change logging information from dev_info() to drm_info().

Signed-off-by: Suraj Upadhyay <usuraj35@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/0d37c7a614eb0885f0f0bed18e48a4d26b345a8e.1594136880.git.usuraj35@gmail.com