arm: mxs: Scrub useless ifdef

As a result of 0defddc8 , which did
a consolidation of the prompt string, this ifdef became empty. Remove
it.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Stefano Babic <sbabic@denx.de>