mimic: Use special rateconv.c license

rateconv.c looks like BSD-2 but it has second clause modified
significantly, therefore be specific about it.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Alistair Francis <alistair.francis@wdc.com>

meta-multimedia/recipes-multimedia/mimic/mimic_1.3.0.1.bb

@@ -7,7 +7,7 @@ SECTION = "multimedia"
 LICENSE = "MIT & \
            PD & \
            CMU-Tex & \
-           BSD & \
+           rateconv & \
            BSD-2-Clause & \
            BSD-3-Clause & \
            flite & \