mmc: Convert ternary operator to str_true_false() helper

Replace direct ternary condition check with existing helper function
str_true_false() to improve code readability and maintain consistency.

Signed-off-by: Li Dong <lidong@vivo.com>
Link: https://lore.kernel.org/r/20250620043517.172705-1-lidong@vivo.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>