omap2plus: voltage: Trivial linking fix 'undefined reference'

LD      init/built-in.o
LD      .tmp_vmlinux1
arch/arm/mach-omap2/built-in.o: In function `omap2_set_init_voltage':
arch/arm/mach-omap2/pm.c:181: undefined reference to `omap_voltage_domain_lookup'
arch/arm/mach-omap2/built-in.o: In function `omap4_twl_init':
arch/arm/mach-omap2/omap_twl.c:244: undefined reference to `omap_voltage_domain_lookup'
arch/arm/mach-omap2/omap_twl.c:247: undefined reference to `omap_voltage_domain_lookup'
arch/arm/mach-omap2/omap_twl.c:250: undefined reference to `omap_voltage_domain_lookup'
make: *** [.tmp_vmlinux1] Error 1

The error is reported when omap2plus_defconfig built with CONFIG_PM disabled
Signed-off-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Thara Gopinath <thara@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Nishanth Menon <nm@ti.com>
Signed-off-by: NKevin Hilman <khilman@ti.com>

arch/arm/plat-omap/include/plat/voltage.h

@@ -65,9 +65,6 @@ struct voltagedomain {
 	char *name;
 };
 
-/* API to get the voltagedomain pointer */
-struct voltagedomain *omap_voltage_domain_lookup(char *name);
-
 /**
  * struct omap_volt_data - Omap voltage specific data.
  * @voltage_nominal:	The possible voltage value in uV
@@ -131,6 +128,9 @@ int omap_voltage_register_pmic(struct voltagedomain *voltdm,
 		struct omap_volt_pmic_info *pmic_info);
 void omap_change_voltscale_method(struct voltagedomain *voltdm,
 		int voltscale_method);
+/* API to get the voltagedomain pointer */
+struct voltagedomain *omap_voltage_domain_lookup(char *name);
+
 int omap_voltage_late_init(void);
 #else
 static inline int omap_voltage_register_pmic(struct voltagedomain *voltdm,
@@ -144,6 +144,10 @@ static inline int omap_voltage_late_init(void)
 {
 	return -EINVAL;
 }
+static inline struct voltagedomain *omap_voltage_domain_lookup(char *name)
+{
+	return ERR_PTR(-EINVAL);
+}
 #endif
 
 #endif