ASoC: msm-cpe: Fix range checking in function fw_name_store

The range checking between "WCD_CPE_IMAGE_FNAME_MAX" and
"copy_count" is off-by-one due to the size of array
"core->dyn_fname" is "WCD_CPE_IMAGE_FNAME_MAX". Subtract
one from the range checking to fix this issue.

Change-Id: I87fd55206f79ad7b13c3878f6642bf5579303b17
Signed-off-by: Xiaoyu Ye <benyxy@codeaurora.org>