No need to try to mount ext4 parttion when a partition is small to handle
a EXT4 file system, when its size is lower than SUPERBLOCK_SIZE.

This patch avoids traces when EFI try to detect FS type on one LBA (512)
partition:

  fs_devread read outside partition 2
  Failed to mount ext2 filesystem..

Change-Id: I852b2b0fb85539e986a45dcfaf765f92e0924536
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/u-boot/+/291860
Reviewed-by: Patrice CHOTARD <patrice.chotard@foss.st.com>
ACI: CITOOLS <MDG-smet-aci-reviews@list.st.com>
ACI: CIBUILD <MDG-smet-aci-builds@list.st.com>
Domain-Review: Patrice CHOTARD <patrice.chotard@foss.st.com>