backlight: apple_bl: use pr_debug()/pr_err() instead of printk()

backlight: apple_bl: use pr_debug()/pr_err() instead of printk()

Use pr_debug()/pr_err() instead of printk() to allow dynamic debugging.
The pr_fmt prefix for pr_ macros is used.  Also fix checkpatch warnings as
below:

WARNING: Prefer pr_debug(... to printk(KERN_DEBUG, ...
WARNING: Prefer pr_err(... to printk(KERN_ERR, ...

[[email protected]: use KBUILD_MODNAME, per Joe]
Signed-off-by: Jingoo Han <[email protected]>
Cc: Matthew Garrett <[email protected]>
Cc: Richard Purdie <[email protected]>
Cc: Joe Perches <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>