tegra2: fix warning: "assert" redefined

Commit 21726a7a "Add assert() for debug assertions" caused build
warnings for all tegra2 based boards:

clock.c:36:1: warning: "assert" redefined
In file included from clock.c:29:
include/common.h:144:1: warning: this is the location of the previous definition
Signed-off-by: NWolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>

arch/arm/cpu/armv7/tegra2/clock.c

@@ -28,14 +28,6 @@
 #include <asm/arch/tegra2.h>
 #include <common.h>
 
-#ifdef DEBUG
-#define assert(x)	\
-	({ if (!(x)) printf("Assertion failure '%s' %s line %d\n", \
-		#x, __FILE__, __LINE__); })
-#else
-#define assert(x)
-#endif
-
 /*
  * Get the oscillator frequency, from the corresponding hardware configuration
  * field.