pinctrl: zynq: Use define directive for PIN_CONFIG_IO_STANDARD

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

drivers/pinctrl/pinctrl-zynq.c:985:18: warning: implicit conversion from
enumeration type 'enum zynq_pin_config_param' to different enumeration
type 'enum pin_config_param' [-Wenum-conversion]
{"io-standard", PIN_CONFIG_IOSTANDARD, zynq_iostd_lvcmos18},
~ ^~~~~~~~~~~~~~~~~~~~~
drivers/pinctrl/pinctrl-zynq.c:990:16: warning: implicit conversion from
enumeration type 'enum zynq_pin_config_param' to different enumeration
type 'enum pin_config_param' [-Wenum-conversion]
= { PCONFDUMP(PIN_CONFIG_IOSTANDARD, "IO-standard", NULL, true),
~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/pinctrl/pinconf-generic.h:163:11: note: expanded from
macro 'PCONFDUMP'
.param = a, .display = b, .format = c, .has_arg = d \
^
2 warnings generated.

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.

Signed-off-by: Nathan Chancellor <[e-mail]>
Acked-by: Michal Simek <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/pinctrl-zynq.c

···
 	zynq_iostd_max
 };
 
-/**
- * enum zynq_pin_config_param - possible pin configuration parameters
- * @PIN_CONFIG_IOSTANDARD: if the pin can select an IO standard, the argument to
+/*
+ * PIN_CONFIG_IOSTANDARD: if the pin can select an IO standard, the argument to
  *	this parameter (on a custom format) tells the driver which alternative
  *	IO standard to use.
  */
-enum zynq_pin_config_param {
-	PIN_CONFIG_IOSTANDARD = PIN_CONFIG_END + 1,
-};
+#define PIN_CONFIG_IOSTANDARD		(PIN_CONFIG_END + 1)
 
 static const struct pinconf_generic_params zynq_dt_params[] = {
 	{"io-standard", PIN_CONFIG_IOSTANDARD, zynq_iostd_lvcmos18},