Convert CONFIG_UBIFS_SILENCE_MSG to Kconfig

Introduce another difference from upstream (kernel) source in
fs/ubifs/super.c: adding preprocessor condition as y variable in
mount_ubifs() depends on CONFIG_UBIFS_SILENCE_MSG:
fs/ubifs/super.c:1337:15: error: variable ?y? set but not used [-Werror=unused-but-set-variable]
  long long x, y;

Not setting CONFIG_UBIFS_SILENCE_MSG in am335x_igep003x_defconfig and
igep0032_defconfig. Although it was defined in their config headers, it
depends on CMD_UBIFS which is not set for them.

Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Heiko Schocher <hs@denx.de>
diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index effa8d9..2c478cb 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1334,7 +1334,10 @@
 static int mount_ubifs(struct ubifs_info *c)
 {
 	int err;
-	long long x, y;
+	long long x;
+#ifndef CONFIG_UBIFS_SILENCE_MSG
+	long long y;
+#endif
 	size_t sz;
 
 	c->ro_mount = !!(c->vfs_sb->s_flags & MS_RDONLY);
@@ -1613,7 +1616,9 @@
 		  c->vi.ubi_num, c->vi.vol_id, c->vi.name,
 		  c->ro_mount ? ", R/O mode" : "");
 	x = (long long)c->main_lebs * c->leb_size;
+#ifndef CONFIG_UBIFS_SILENCE_MSG
 	y = (long long)c->log_lebs * c->leb_size + c->max_bud_bytes;
+#endif
 	ubifs_msg(c, "LEB size: %d bytes (%d KiB), min./max. I/O unit sizes: %d bytes/%d bytes",
 		  c->leb_size, c->leb_size >> 10, c->min_io_size,
 		  c->max_write_size);