arm: ti: Add missing "=" from previous fix

While the original patch to fix a regression in distro boot for mmc on
these platforms had the correct syntax, I broke the change while
applying.  Add back in the missing "=" here so that the syntax is
correct.

Reported-by: Andre Heider <a.heider@gmail.com>
Fixes: 27e0f3bc ("arm: ti: Fix regression in distro boot for mmc")
Signed-off-by: Tom Rini <trini@konsulko.com>