dsp: q6adm: Resolve mem corruption in adm cb

Conversion of negative "num_modules" var value
will result in max possible unsigned int value
and hence can cause mem corruption when accessed.

Resolve this by assigning the same data type
to "num_modules" var as used in the calling fn.

Change-Id: I4c9d7215b9c7345637e1eb3a1992a41fef71c5cb
Signed-off-by: Soumya Managoli <quic_c_smanag@quicinc.com>