stm32: spi: fix link to bug in comments
stm32: spi: fix link to bug in comments

Wrong link makes it harder to find the issue at hand, fix the URL

BRANCH=none
BUG=b:35539666
TEST=none

Change-Id: I71bb069c43e540d101cdb60d6fa6f5d4e90a4d13
Signed-off-by: Nicolas Norvez <3001a977f47a2bc94ec05551872e2ce88b323556@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1481661
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>

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