backlight: ams369fg06: remove unnecessary NULL deference check

Remove unnecessary NULL deference check, because it was already checked in
ams369fg06_probe().  Also, unnecessary parentheses are removed in
ams369fg06_power_is_on().

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>