fix(dracut.sh): kmoddir does not handle trailing /

Fixes #2236

+(/) only works in bash interactive mode. Using any non-interactive
bash run simply doesn't remove anything.

The solution is copied from dracut-lib.sh, trim().

Author: pvalena

dracut.sh

@@ -1033,7 +1033,7 @@ stdloglvl=$((stdloglvl + verbosity_mod_l))
 ((stdloglvl < 0)) && stdloglvl=0
 
 [[ $drivers_dir_l ]] && drivers_dir=$drivers_dir_l
-drivers_dir="${drivers_dir%%+(/)}"
+drivers_dir="${drivers_dir%"${drivers_dir##*[!/]}"}"
 [[ $do_strip_l ]] && do_strip=$do_strip_l
 [[ $do_strip ]] || do_strip=yes
 [[ $aggressive_strip_l ]] && aggressive_strip=$aggressive_strip_l