fs_mgr: Fix return in error case

We were doing "return -1" in an error case from a function that
returns bool.  Since it's non-zero, this gets implicitly cast to
'true', which almost certainly isn't what we wanted here.

Test: TreeHugger
Change-Id: I76c188c22d907fc425cf4d5b0b1575f640a78ee3
1 file changed