docs: fix simple typo, accumlate -> accumulate

There is a small typo in CMSIS/DSP/Source/FilteringFunctions/arm_conv_fast_opt_q15.c, CMSIS/DSP/Source/FilteringFunctions/arm_conv_opt_q15.c, CMSIS/DSP/Source/FilteringFunctions/arm_conv_opt_q7.c, CMSIS/DSP/Source/FilteringFunctions/arm_conv_partial_fast_opt_q15.c, CMSIS/DSP/Source/FilteringFunctions/arm_conv_partial_opt_q15.c, CMSIS/DSP/Source/FilteringFunctions/arm_conv_partial_opt_q7.c, CMSIS/DSP/Source/FilteringFunctions/arm_correlate_fast_opt_q15.c, CMSIS/DSP/Source/FilteringFunctions/arm_correlate_opt_q15.c, CMSIS/DSP/Source/FilteringFunctions/arm_correlate_opt_q7.c.

Should read `accumulate` rather than `accumlate`.