scripts: setlocalversion: fix a bashism

Fix bashism reported by checkbashisms by using only one '=':

possible bashism in scripts/setlocalversion line 96 (should be 'b = a'):
	if [ "`hg log -r . --template '{latesttagdistance}'`" == "1" ]; then

Fixes: 38b3439d ("setlocalversion: update mercurial tag parsing")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Mike Crowe <mcrowe@zipitwireless.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>