backlight: mp3309c: Initialize backlight properties without memset

backlight: mp3309c: Initialize backlight properties without memset

Assigning values to a struct using a compound literal (since C99) also
guarantees that all unspecified struct members are empty-initialized, so
it properly replaces the memset to zero.

The code looks a bit nicer and more idiomatic (though that might be
subjective?). The resulting binary is a bit smaller. On ARCH=arm with
an allnoconfig + minimal changes to enable the mp3309c driver the
difference is 12 bytes.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Tested-by: Flavio Suligoi <f.suligoi@asem.it>
Reviewed-by: Daniel Thompson (RISCstar) <danielt@kernel.org>
Link: https://lore.kernel.org/r/14514a1b0d3df6438aa10bb74f1c4fc2367d9987.1751361465.git.u.kleine-koenig@baylibre.com
Signed-off-by: Lee Jones <lee@kernel.org>