power: supply: axp20x_usb_power: Fix typo in VBUS current limit macros

The VBUS current limit value macros have VBUS typed as VBUC, while
the bitmask macro is named correctly. Fix it.

Fixes: 69fb4dca ("power: Add an axp20x-usb-power driver")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>