pk: minor fixes (guards and a wrong assignment)

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/pk.c b/library/pk.c
index 47c19b2..826c29a 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -227,7 +227,7 @@
 
     return 0;
 }
-#endif /* MBEDTLS_PK_USE_PSA_EC_PUB_KEY */
+#endif /* MBEDTLS_PK_USE_PSA_EC_DATA */
 
 #if defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
 /*