Fix compilation with ccache enabled

When ccache is enabled the CROSS_COMPILE variable contains a space, so
it must be properly quoted.

Signed-off-by: Doug Kehn <rdkehn@yahoo.com>

Index: cryptodev-linux-1.7/Makefile
===================================================================
--- cryptodev-linux-1.7.orig/Makefile
+++ cryptodev-linux-1.7/Makefile
@@ -18,7 +18,7 @@ ifneq (${ARCH},)
 KERNEL_MAKE_OPTS += ARCH=${ARCH}
 endif
 ifneq (${CROSS_COMPILE},)
-KERNEL_MAKE_OPTS += CROSS_COMPILE=${CROSS_COMPILE}
+KERNEL_MAKE_OPTS += CROSS_COMPILE="${CROSS_COMPILE}"
 endif
 
 build: version.h