tools/install_kernel.sh: fix bashisms

voodoo@hestia:/opt/github/stable-kernel$ ./checkbashisms tools/install_kernel.sh
script tools/install_kernel.sh does not appear to be a /bin/sh script
possible bashism in tools/install_kernel.sh line 31 (should be '.', not 'source'):
source ${DIR}/version.sh
possible bashism in tools/install_kernel.sh line 77 (should be '.', not 'source'):
                source "${location}/SOC.sh"
possible bashism in tools/install_kernel.sh line 148 ('((' should be '$(('):
        for (( c=1; c<=${num_partitions}; c++ ))
possible bashism in tools/install_kernel.sh line 188 ('((' should be '$(('):
        for (( c=1; c<=${NUM_MOUNTS}; c++ ))
possible bashism in tools/install_kernel.sh line 191 (should be >word 2>&1):
                sudo umount ${DRIVE} &> /dev/null || true
possible bashism in tools/install_kernel.sh line 215 (read with option other than -r):
                read -p "Are you 100% sure, on selecting [${MMC}] (y/n)? "
possible bashism in tools/install_kernel.sh line 215 (read without variable):
                read -p "Are you 100% sure, on selecting [${MMC}] (y/n)? "
possible bashism in tools/install_kernel.sh line 216 (should be 'b = a'):
                [ "${REPLY}" == "y" ] && unmount_partitions
possible bashism in tools/install_kernel.sh line 232 (should be '.', not 'source'):
        source ${DIR}/system.sh
possible bashism in tools/install_kernel.sh line 236 (should be 'b = a'):
                if [ "x${MMC}" == "x" ] ; then
possible bashism in tools/install_kernel.sh line 240 (alternative test command ([[ foo ]] should be [ foo ])):
                        if [[ "${MMC}" =~ "mmcblk" ]] ; then

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>