recovery-initramfs: fix multi-MTD detection when formatting NAND partitions

Commit 7e81e706a1 modified the logic used to
determine if a NAND is using multi-MTD or single-MTD, but single quotes were
used in the grep pattern, which prevents the variable inside from expanding.
This makes the script always enter the single-MTD code path, even in multi-MTD
systems, which breaks partition formatting in these cases.

Replace the single quotes with double quotes so the variable can expand and the
condition can be properly checked.

https://onedigi.atlassian.net/browse/DEL-8773

Signed-off-by: Gabriel Valcazar <gabriel.valcazar@digi.com>

meta-digi-dey/recipes-core/recovery/recovery-initramfs/recovery-initramfs-init

@@ -233,7 +233,7 @@ format_ubi_volume() {
 
 	# If the system is a multi-MTD, there must be an MTD partition by the
 	# same name as the UBI volume
-	result="$(grep '\"${1}\"$' /proc/mtd)"
+	result="$(grep "\"${1}\"$" /proc/mtd)"
 	if [ -n "${result}" ]; then
 		# Find the MTD partition.
 		local mtd_num="$(sed -ne "s/mtd\([0-9]\+\):.*\<${1}\>.*/\1/g;T;p" /proc/mtd 2>/dev/null)"