dsp: Fix a memory leak issue when nvmem read returns invalid length

When nvmem cell read returns invalid length the allocated buffer
is not freed. Free the buffer in this scenario to fix
memory leak issue.

Change-Id: I2e0010c1cfb2ea03cb4f25abf55e94ce4f0c5fcf
Signed-off-by: Aditya Bavanari <abavanar@codeaurora.org>