buildroot

ux500-firmware: use $(TARGET_MAKE_ENV) when calling $(MAKE)

And remove whitespace.

Signed-off-by: Gustavo Zacarias <gustavo.zacarias@free-electrons.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>