initramfs-framework: remove hard dependency with busybox

initramfs-framework: remove hard dependency with busybox

In 'finish'script the Switch_root command with option -c is busybox specific.
When package-core-base-utils is selected the boot is breaking with message
"Switch_root: invalid option — ‘c’.It was reproduced using qemu.
Remove -c option to make it compatible with both providers.
It is tested using qemu with busybox and package-core-base-utils. In both cases
qemu boots successfully and filesystem is accessible.
Fixes [YOCTO #15716]

CC: Yoann Congal <yoann.congal@smile.fr>
CC: Randy MacLeod <randy.macleod@windriver.com>
CC: jbk <jbk@mm-software.com>
CC: Raj Khem <raj.khem@gmail.com>
CC: Adrian Freihofer <adrian.freihofer@gmail.com>
Signed-off-by: Christos Gavros <gavrosc@yahoo.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>