Correct typo in variable name

This goes along with https://github.com/AOKP/hardware_qcom_media/commit/0428e4efb7e59ce365032beb9fb348f98b70d93d

We may want to revert it, if we pick commits from codeaurora.

Change-Id: I4cbc71103e76b1d4d2bc033d6cac17b63bf84620
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
arch/arm/Makefile: Enable pipe compiling

-pipe

Use pipes rather than temporary files for communication between the various stages of
compilation. This fails to work on some systems where the assembler is unable to read
from a pipe; but the GNU assembler has no trouble.