mtd: Fix get_mtdparts()

When ENV_IS_IN_UBI is enable, get_mtdparts is called before relocation.

During first get_mtdparts() call, mtdparts is not available in environment,
it can be retrieved by calling board_mtdparts_default(), but following
env_set() do nothing as we are before relocation. Finally mtdparts is
still not available in environment.

At second get_mtdparts() call, use_defaults is false, but mtdparts is still
not in environment and is NULL.

Remove use_defaults bool, only mtdparts criteria is useful.

Fixes: commit 5ffcd50612f6 ("mtd: Use default mtdparts/mtids when not defined
in the environment")

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/mtd/mtd_uboot.c b/drivers/mtd/mtd_uboot.c
index d638f70..0a41ed4 100644
--- a/drivers/mtd/mtd_uboot.c
+++ b/drivers/mtd/mtd_uboot.c
@@ -122,7 +122,6 @@
 {
 	__maybe_unused const char *mtdids = NULL;
 	static char tmp_parts[MTDPARTS_MAXLEN];
-	static bool use_defaults = true;
 	const char *mtdparts = NULL;
 
 	if (gd->flags & GD_FLG_ENV_READY)
@@ -130,7 +129,7 @@
 	else if (env_get_f("mtdparts", tmp_parts, sizeof(tmp_parts)) != -1)
 		mtdparts = tmp_parts;
 
-	if (mtdparts || !use_defaults)
+	if (mtdparts)
 		return mtdparts;
 
 #if defined(CONFIG_SYS_MTDPARTS_RUNTIME)
@@ -144,8 +143,6 @@
 	if (mtdparts)
 		env_set("mtdparts", mtdparts);
 
-	use_defaults = false;
-
 	return mtdparts;
 }