chipset: convert reset_log_mutex to use K_MUTEX_DEFINE
chipset: convert reset_log_mutex to use K_MUTEX_DEFINE

Using K_MUTEX_DEFINE() initializes the mutex automatically, thus
removing the requirement to use k_mutex_init().

BUG=b:177677037
BRANCH=none
TEST=zmake testall && make buildall

Signed-off-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Change-Id: Icd52129fe6a3edd497a6663b3ffea10c5b7b9dce
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2782233
Reviewed-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec