configs/raspberrypi2: kernel version does not exist anymore

It looks like version 23c76b7 of Raspberry kernel does not exist
anymore:

$ git clone https://github.com/raspberrypi/linux.git
[...]
$ cd linux
$ git co 23c76b7f608e51258c6fca02aebeb5d588583149
fatal: reference is not a tree: 23c76b7f608e51258c6fca02aebeb5d588583149

Replace it by latest version of 3.19 branch.

[Thomas: tweak commit log.]

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

configs/raspberrypi2_defconfig

@@ -15,7 +15,7 @@ BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_19=y
 BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_GIT=y
 BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/raspberrypi/linux.git"
-BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="23c76b7f608e51258c6fca02aebeb5d588583149"
+BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="2c4959b772a35d9d459b0a92f39bb066e9a44d37"
 BR2_LINUX_KERNEL_DEFCONFIG="bcm2709"
 BR2_LINUX_KERNEL_ZIMAGE=y