regulator: mcp16502: add enum MCP16502_REG_HPM description

Add description for MCP16502_REG_HPM to prevent a kernel-doc warning:

drivers/regulator/mcp16502.c:90: warning: Enum value 'MCP16502_REG_HPM' not described in enum 'mcp16502_reg'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20230117070139.28905-1-rdunlap@infradead.org


Signed-off-by: Mark Brown <broonie@kernel.org>