feat(st-regulator): improve out of memory message

Improve out of memory message when to many regulators try to register.

Signed-off-by: Pascal Paillet <p.paillet@st.com>
Change-Id: I4fc4db87a6364bbc8f429796cbf03807865c612d
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/271770
Reviewed-by: CITOOLS <MDG-smet-aci-reviews@list.st.com>
Reviewed-by: CIBUILD <MDG-smet-aci-builds@list.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@foss.st.com>
Reviewed-by: Sebastien PASDELOUP <sebastien.pasdeloup-ext@st.com>
Domain-Review: Yann GAUTIER <yann.gautier@foss.st.com>

drivers/regulator/regulator_core.c

@@ -811,7 +811,7 @@ int regulator_register(const struct regul_description *desc, int node)
 	}
 
 	if (rdev == rdev_array + PLAT_NB_RDEVS) {
-		WARN("out of memory\n");
+		WARN("Not enough place for regulators, PLAT_NB_RDEVS should be increased.\n");
 		return -ENOMEM;
 	}