mfd: axp20x: Correct name of temperature data ADC registers

The registers 0x56 and 0x57 of AXP22X PMIC store the value of the
internal temperature of the PMIC.

This patch modifies the name of these registers from AXP22X_PMIC_ADC_H/L
to AXP22X_PMIC_TEMP_H/L so their purpose is clearer.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>