fix: lvm2 modprobe path

LVM2 configure uses `AC_PATH_TOOL` to find modprobe path if not set, as
we're building inside tools it was picking up `/toolchain/bin/modprobe`.
Explicitly set `MODPROBE_CMD=/sbin/modprobe` to the path of `modprobe`
binary in talos.

Fixes: siderolabs/talos#9300

Signed-off-by: Noel Georgi <git@frezbo.dev>

lvm2/pkg.yaml

@@ -36,7 +36,8 @@ steps:
              --enable-udev_sync \
              --enable-udev_rules \
              --enable-static_link \
-             --with-udev-prefix=/usr
+             --with-udev-prefix=/usr \
+             MODPROBE_CMD=/sbin/modprobe
 
         rm -f /sbin/blkdeactivate \
               /sbin/fsadm \