pinctrl: nomadik: follow conditional kernel coding conventions

Fix strict checkpatch warnings relative to if-else blocks and bool
expressions. Message types addressed:

   CHECK: Comparison to NULL could be written "!nmk_cfg_params[index].choice"
   CHECK: Unbalanced braces around else statement
   CHECK: Using comparison to false is error prone
   CHECK: Using comparison to true is error prone
   CHECK: braces {} should be used on all arms of this statement

Before: 0 errors, 1 warnings, 16 checks.
After:  0 errors, 1 warnings,  7 checks.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Link: https://lore.kernel.org/r/20240228-mbly-gpio-v2-13-3ba757474006@bootlin.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>