=INT(CONVERT(D6,"m","ft"))&"'"&ROUNDDOWN(MOD(CONVE RT(D6,"m","ft"),1)*12,0)&""""
will round the inches down.

If rounding down is acceptable, here is a (far more cryptic to decipher)
formula that is 12 characters shorter than yours (well, actually 13
characters shorter if you remove the "neatening up" space that I placed
between the feet and inches sections)...

=TEXT(CONVERT(D6,"m","ft")-MOD(CONVERT(D6,"m","ft"),1)/2,"d' h\""")

Rick