pinctrl: qcom: sdm845: Fix CONFIG preprocessor guard

Clang warns when CONFIG_ACPI is unset:

 drivers/pinctrl/qcom/pinctrl-sdm845.c:1320:5: warning: 'CONFIG_ACPI' is
 not defined, evaluates to 0 [-Wundef]
 #if CONFIG_ACPI
     ^
 1 warning generated.

Use ifdef instead of if to resolve this.

Fixes: a229105d

 ("pinctrl: qcom: sdm845: Provide ACPI support")
Link: https://github.com/ClangBuiltLinux/linux/issues/569
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>