Slightly change bl (battery level) when used in an enum: if the enum contained 10...

Slightly change bl (battery level) when used in an enum: if the enum contained 10 items, bl would return 11 if the battery level was 100 percent (the enum would then display the last entry). Now bl returns a value within the given range. Themes may need to be updated to look as intended.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@27784 a1c6a512-1295-4272-9138-f99709370657