main/busybox-initscripts: fix xvd* cdrom symlink

Fix arithmetic syntax error for xvd* disks that does not have
capabilities.

fixes #13203

main/busybox-initscripts/APKBUILD

@@ -2,7 +2,7 @@
 # Maintainer: Natanael Copa <ncopa@alpinelinux.org>
 pkgname=busybox-initscripts
 pkgver=4.0
-pkgrel=3
+pkgrel=4
 pkgdesc="Init scripts for busybox daemons"
 url="https://git.alpinelinux.org/aports/tree/main/busybox-initscripts"
 arch="noarch"
@@ -66,5 +66,5 @@ acbba3385fb2c416362eb9176f24146b617a2e394ee0e00b9eff89350f82468a5ab8396f4f52b0aa
 e5433414c7a6d7e77819e4e9e98c4855b97e7e344201aa29189d00124b97050f480787af3992d099ffa67485557fffb8ec1afd79b2be420ba7012cd1bfa8fff1  mdev.conf
 ebd82f935da2ca89097234dd8a8f47e179a423652c151123a1f3343f3e1e7bfaba2b8800380e988d4e8f4294545d3a9ab6708ae2e77c5b108b5f091bbce8f94a  dvbdev
 b2dcf0ded9264334d79fbbb05dd12d649dc3119a060db5893f0e8aeca2141323961c3ba4c822a0ffb00dba848742d5cb374dc77e776b57cecde352a3e8e30f8a  usbdev
-cf5301b2a510126be5442a7c65d7198d1c96703ed9e228352cd6aac9d167d8d79a1fdf7203c11a0b59842fad1eee51ddb0dc964a8e069391953d4cbe47fb98ec  persistent-storage
+0f54666072a8ee32965cc1b5205a6d35bc2ba6655f298c37ba9ccd72949fa7c41b1e540ec91f41b11f4b261ace614cdcc42dccf390bf0a22698d0ba499feae39  persistent-storage
 "

main/busybox-initscripts/persistent-storage

@@ -10,8 +10,8 @@ symlink_action() {
 # cdrom symlink
 case "$MDEV" in
 	sr*|xvd*)
-		caps="0x$(cat /sys/block/$MDEV/capability)"
-		if [ $(($caps & 8)) -gt 0 ]; then
+		caps="$(cat /sys/block/$MDEV/capability 2>/dev/null)"
+		if [ $(( 0x${caps:-0} & 8 )) -gt 0 ]; then
 			symlink_action $MDEV cdrom
 		fi
 esac