linux_compat: fix potential NULL pointer access

malloc_cache_aligned() might return zero, so fix potential NULL pointer
access if __GFP_ZERO flag is set.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Ralph Siemsen <ralph.siemsen@linaro.org>
diff --git a/lib/linux_compat.c b/lib/linux_compat.c
index 6373b44..81ea8fb 100644
--- a/lib/linux_compat.c
+++ b/lib/linux_compat.c
@@ -20,7 +20,7 @@
 	void *p;
 
 	p = malloc_cache_aligned(size);
-	if (flags & __GFP_ZERO)
+	if (p && flags & __GFP_ZERO)
 		memset(p, 0, size);
 
 	return p;