charger: add locale global variable

Some functions in minui reference a global extern char *locale.  None
of them are used by charger, but the bfd linker cannot optimize them
out and fails to link charger.  Define char *locale in charger.c
so it can resolve the symbol.

Change-Id: I738daf95d24356bf96bd226d91a5dc64b5d4dc9b

Conflicts:
	charger/charger.c