u-boot-fslc: Update revision to e3517cb

This includes following fixes:

e3517cb wandboard: Changed mmcroot variable so kernel 3.10.31 boots
2082e4d iMX6: Change mmcroot to use fixed mmc block index for USDHC

The patch iMX6-Change-mmcroot-to-use-fixed-mmc-block-index-for.patch
is now applied in the repository, so removed from the metadata.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>