linux-sysmocom: Remove the branch from the SRC_URI

9610e792ffde7fb2599d19ca6d2a03230f2043c6 can not be found
in the linux-3.10.76 branch. Just avoid this branch game.

ERROR: Fetcher failure: Unable to find revision 9610e792ffde7fb2599d19ca6d2a03230f2043c6 in branch linux-3.10.76 even from upstream
ERROR: Function failed: Fetcher failure for URL: 'git://git.sysmocom.de/sysmo-bts/linux.git;protocol=git;branch=linux-3.10.76'. Unable to fetch URL from any source.
ERROR: Logfile of failure stored in: /home/builder/jenkins/workspace/Yocto-Master/label/OE/build/tmp/work/sysmobts_v2-poky-linux-gnueabi/linux-sysmocom/3.10.76+gitAUTOINC+9610e792ff-r43/temp/log.do_fetch.16350
NOTE: recipe linux-sysmocom-3.10.76+gitAUTOINC+9610e792ff-r43: task do_fetch: Failed
ERROR: Task 126 (/home/builder/jenkins/workspace/Yocto-Master/label/OE/meta-sysmocom-bsp/recipes-bsp/linux/linux-sysmocom_git.bb, do_fetch) failed with exit code '1

recipes-bsp/linux/linux-sysmocom_git.bb

@@ -18,7 +18,7 @@ SRCREV = "9610e792ffde7fb2599d19ca6d2a03230f2043c6"
 PR = "r43"
 PV = "${LINUX_VERSION}+git${SRCPV}"
 
-SRC_URI = "git://git.sysmocom.de/sysmo-bts/linux.git;protocol=git;branch=linux-3.10.76 \
+SRC_URI = "git://git.sysmocom.de/sysmo-bts/linux.git;protocol=git \
 	   file://defconfig"
 
 S = "${WORKDIR}/git"