extcon: arizona: Deobfuscate arizona_extcon_do_magic

arizona_extcon_do_magic does not lend a lot of clarity to the purpose
of the function, and as all the registers used are described in the
datasheet there is no need to obfuscate the code. This patch renames the
function to arizona_extcon_hp_clamp, as it controls clamping on the
headphone output.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>