Unless specified in the environment, $(CC) expands to some generic
host C compiler like cc or c99. We set our own value for $(CC), but
only few lines later.

Move the first use of the $(CC) variable behind the definition to
correct this.

Change-Id: I45344e063d21ddfe22b7ad77954e85c1c46087bd
Fixes: 1684b8733 ("Use clang assembler when clang compiler is used")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>