thin-provisioning-tools: use sh on path when invoking txt2man

txt2man contains a test which might try to use ksh to run the script, so we
avoid running /bin/sh.

Upstream-Status: Inappropriate [oe specific]

Signed-off-by: joe.slater <joe.slater@windriver.com>

--- a/Makefile.in
+++ b/Makefile.in
@@ -210,7 +210,7 @@ endif
 
 %.8: %.txt bin/txt2man
 	@echo "    [txt2man] $<"
-	$(V) bin/txt2man -p -t $(basename $(notdir $<)) $< > $@
+	$(V) sh bin/txt2man -p -t $(basename $(notdir $<)) $< > $@
 
 #----------------------------------------------------------------