c-icap: fix incorrect dependency on BR2_PREFER_STATIC_LIB

BR2_PREFER_STATIC_LIB has been changed/renamed quite some time ago to
BR2_STATIC_LIBS, but the c-icap submission was done before that, and
during the review/merge of the patch, this rename was forgotten.

This commit therefore fixes the c-icap dependency on BR2_STATIC_LIBS,
which should fix:

  http://autobuild.buildroot.net/results/cb623460de30dd7c4ef3275fe13220c1ca0642a5/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/c-icap/Config.in

@@ -1,6 +1,6 @@
 config BR2_PACKAGE_C_ICAP
 	bool "c-icap"
-	depends on !BR2_PREFER_STATIC_LIB
+	depends on !BR2_STATIC_LIBS
 	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on BR2_USE_MMU # fork()
 	help
@@ -15,4 +15,4 @@ config BR2_PACKAGE_C_ICAP
 
 comment "c-icap needs a toolchain w/ threads and dynamic library"
 	depends on BR2_USE_MMU
-	depends on BR2_PREFER_STATIC_LIB  || !BR2_TOOLCHAIN_HAS_THREADS
+	depends on BR2_STATIC_LIBS || !BR2_TOOLCHAIN_HAS_THREADS