pinctrl: max77620: Use define directive for max77620_pinconf_param values

Clang warns when one enumerated type is implicitly converted to another:

drivers/pinctrl/pinctrl-max77620.c:56:12: warning: implicit conversion
from enumeration type 'enum max77620_pinconf_param' to different
enumeration type 'enum pin_config_param' [-Wenum-conversion]
                .param = MAX77620_ACTIVE_FPS_SOURCE,
                         ^~~~~~~~~~~~~~~~~~~~~~~~~~

It is expected that pinctrl drivers can extend pin_config_param because
of the gap between PIN_CONFIG_END and PIN_CONFIG_MAX so this conversion
isn't an issue. Most drivers that take advantage of this define the
PIN_CONFIG variables as constants, rather than enumerated values. Do the
same thing here so that Clang no longer warns.

Link: https://github.com/ClangBuiltLinux/linux/issues/139


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>