target/linux: replace egrep with grep -E

egrep is deprecated and replaced by grep -E. The latter is used
throughout the tree.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

target/linux/ipq806x/base-files/lib/upgrade/linksys.sh

@@ -9,7 +9,7 @@ linksys_get_target_firmware() {
 	cur_boot_part=$(/usr/sbin/fw_printenv -n boot_part)
 	if [ -z "${cur_boot_part}" ] ; then
 		mtd_ubi0=$(cat /sys/devices/virtual/ubi/ubi0/mtd_num)
-		case $(egrep ^mtd${mtd_ubi0}: /proc/mtd | cut -d '"' -f 2) in
+		case $(grep -E ^mtd${mtd_ubi0}: /proc/mtd | cut -d '"' -f 2) in
 		kernel1|rootfs1)
 			cur_boot_part=1
 			;;